1. Open Real Time > Settings.
2. Under Realtime Fulfilment Days, switch on each weekday you want to serve.
3. In the Times section a block appears for each enabled day. Click Add New to add a window; a row with Start (default 09:00) and End (default 17:00) time pickers appears.
4. Adjust the times. Add more rows with Add New if you have split hours (for example 11:00-14:00 and 17:00-21:00). Remove a row with Delete.
5. Set the Order Buffer Time (minutes) and click Save.

Customers can then only pick a time that falls inside one of that weekday's windows (shifted by the buffer), and never earlier than now + buffer.