As a new technical lead in a new company, what are some additional strategies to employ to change the culture of the development team so that people show up at the time that I've requested?

TLDR: My team doesn't show up on time. I've tried to compel them and it isn't working.

Background Data:

Small company, 30 employees, 5 members of my team. The previous lead is still on staff as a regular developer. The culture prior to my arrival was one of informality with no set boundaries or core hours. This culture was not challenged by the corporate leaders. Most people on the team would show up between 10:30 and 11:00 because of this. Other departments, due to the nature of their work, have set start times of either 8 or 9.

This discrepancy and unpredictability causes a lot of angst between my department and other departments. As such, I sat the team down and specified a 'no later than' time of 9:30. I explained my reasoning and I explained the benefits of such a scheme and the negatives of the current scheme. It was a long and contentious conversation and 3 of the 5 people on the team were quite displeased.

Needless to say, people aren't showing up on time (and 9:35 is not on time.)

I've scheduled our daily standup meeting at 9:30 as an added motivator. Knowing that it takes a little bit of time to transition start times (with commute, etc...) I initially would wait to begin the meeting until everyone showed up, but now I just start the meeting (and often finish the meeting) with whomever is present. That seems to not be making a difference either and it's making the team less cohesive.

Conversations on an individual and group basis yield the same results as the original conversation (i.e. they don't see the value, think I'm taking away a perk of the job, etc...)

I have the full support and backing of the senior management team and am empowered to employ whatever devices I feel appropriate to get this taken care of.

My current next step is to send someone home and make them take the day off. Is that too drastic? Are there alternative strategies that I'm overlooking that could help me solve this problem?

Edit based on questions in Jarrod's answer

How new of a technical lead? 6 months, at this company, at the time of this question.

Why are you imposing purely non-technical managerial policies? It is in the scope of my position as defined by executive management.

What are your management credentials? 10 years experience as a technical lead. No formal education or certification in anything managerial.

What previous personnel management experience do you have? I have been a technical lead for 10 years. I've been responsible for hiring/firing/interviewing/reviewing/leading/building a few different technical teams.

Have you earned the respect of the team in a technical manner? Yes

Have you earned the respect of the team in a managerial manner? I was interviewed for technical and managerial ability by the team. I was clear and straightforward about how I like to run technical teams and how I like to run projects (with the obvious caveat that that is just a starting point and culture and personnel ultimately influence where I land.) There are many things, from a managerial perspective, that the team is quite happy with.

Did the previous technical lead step down? Yes.

Was the previous technical lead demoted? No. It was his request.

Was the previous technical lead effective? For a time. But, growth of the company and the codebase made his style ineffective.

Does the majority of the existing team have a more personal relationship with the previous technical lead? Yes.

Is the previous technical lead effectively still in charge? No.

Then [the previous culture of informality with no set boundaries] must have been working? It worked for a time, when the company was still a startup. It has grown and evolved well beyond the startup phase and, due to that growth, is not nearly as effective as it once was. Especially as other departments have introduced a bit more formality and predictability.

Was the team successful in delivering useful products when promised? At the beginning. But, as the company and the product grew, quality and delivery times slipped significantly.

Doesn't sound like you even considered or explored some kind of compromise with your team or the external teams based on their negative feed back. Did you? Of course I have, I'm not a rookie. The fact of the matter is, I respect the fact that the rest of the company works in an inflexible box due to the nature of their responsibilities. The team was unwilling to compromise on their flex time and, in many cases, the other departments are unable to compromise. I have also addressed the negative feedback specifically with the other departments and implemented a number of things to make things better. One of the big benefits of this change was to improve predictability and change perceptions.

Final Update

From the original crew of 5, 2 have been replaced. The first was the previous team lead. We could not see eye-to-eye on how to run development projects and he could not accept changes to what he had previously laid down, so we mutually agreed to part ways. The second lost interest in the work, made a couple of big mistakes and we also mutually agreed to part ways.

The team, as a whole, now shows up early enough to ensure plenty of coverage for the rest of the company. What ultimately worked was mandate and peer pressure. In addition, other changes that have been instituted have resulted in nearly all of the inter-departmental angst to be resolved. Everyone still gets to work on awesome projects, mostly of their choosing, at their own pace at an exciting company and they are all quite content despite the job market being ridiculous in the area.

I have been promoted to an executive position and the new 'problem team' has been moved under me (in addition to still retaining control of the dev team and still developing.) I'm now working to help them perform better and be better teammates to their colleagues. I don't have the punctuality issue with this new team... Their issues are accuracy and communication.