Each model has her own schedule, in Models → your model → Schedule tab.
The timezone first
Start by checking the Timezone: all time slot hours are interpreted in that timezone. It's also what the AI uses to place the conversation within the day (good morning or good evening, weekend references, and so on).
24/7 Mode or time slots
24/7 Mode (the default setting): the AI replies around the clock.
Time slots: turn off 24/7 Mode and add a time slot for each window where the AI is allowed to reply, day by day (for example Monday 9 AM to 11 PM). Outside of them, it stays silent. Each time slot can be enabled or disabled without being deleted.
What happens outside the time slots
The AI sends no messages outside a time slot, neither replies nor nudges. Messages received during that time aren't lost: as soon as the slot starts again, the AI picks up the waiting conversations and replies to the fans who wrote in the meantime.
Why set a schedule
A believable schedule strengthens realism: a creator who replies at 4 AM every single day ends up raising suspicions. Schedules also let you set aside windows where your team handles the conversations itself.