The delays have already begun, but now the MTA has a detailed map that outlines what to expect from now through summer 2020:

With the revised approach, L customers will have normal service during the highest ridership times.

Weeknights: 8 PM to 5 AM L trains run every 20 minutes between Brooklyn and Manhattan and every 10 minutes within Brooklyn. Service will ramp down starting at 8 PM to make room for work trains. Overnight, between 1:30 AM and 5 AM, the service runs at its normal frequency, with L trains running every 20 minutes.

Weekends: 8 PM Friday until 5 AM Monday, L trains run 20 minutes between Brooklyn and Manhattan, and every 10 minutes within Brooklyn. Overnight, between 1:30 AM and 5 AM, service runs at its normal frequency, with L trains running every 20 minutes.

L trains will run every 10 minutes within Brooklyn thanks to extra “overlay” trains between Lorimer St and Canarsie-Rockaway Pkwy. We’ll be running these trains during the busiest times L service is impacted by tunnel work (10 PM- 1:30 AM weeknights and 6 AM to 1:30 AM weekends). Service on the L will be reduced nights and weekends. We’ll be enhancing M, G, 7, and bus service to provide alternatives.