When may the pitch be rolled during a match?

The pitch must not be rolled during the match except as Law 9.1 allows:

• Before each innings (other than the first) and before each day's play after the first: up to 7 minutes, at the request of the batting captain.
• After a delayed start: if the start is delayed after the toss and before the first innings, the batting captain may ask for up to 7 minutes extra. The umpires must refuse if they agree the delay hasn't significantly affected the pitch.
• Choice of roller: if more than one roller is available, the batting captain chooses.
• Timing: rolling before play on any day must start no more than 30 minutes before the scheduled (or rescheduled) start. The batting captain may delay it until no less than 10 minutes before the start.

The order before play each day is: mow the pitch (finished at least 30 minutes before the start), clear debris, then roll.

These are the Laws' defaults. A competition's own playing conditions can vary them, and where they do, those apply.