Add a stasis effect on the bottle maybe. Anything put inside (for example, bugs) stays as it was when you corked it for as long as it remains sealed. A sentient being put inside would experience no time passing from the closing to its opening again. (Hrmmmm... plot hook: a wizard is trying to reverse engineer how the bottle works to build prisons for exceedingly powerful inmates. If no time passes they can't try to escape.) If you wanted to soften this, you could merely say that anything in the bottle needs no sustenance or air, and does not age. (This could still result in boredom-maddened creatures being released upon opening).