Tried to work out when is the latest time that the pitch can be changed. I have presumed that the match begins at the toss (as that is when the team sheets are exchanged and therefore sides are locked in), and therefore the pitch must have been nominated and all prep work finished at that time.
6.3 Selection and preparation
Before the match, the Ground Authority shall be responsible for the selection and preparation of the pitch. During the match, the umpires shall control its use and maintenance.
6.4 Changing the pitch
The pitch shall not be changed during the match unless the umpires decide that it is dangerous or unreasonable for play to continue on it and then only with the consent of both captains.
9.1.4 Timing of permitted rolling
The rolling permitted (maximum 7 minutes) before play begins on any day shall be started not more than 30 minutes before the time scheduled or rescheduled for play to begin. The captain of the batting side may, however, delay the start of such rolling until not less than 10 minutes before the time scheduled or rescheduled for play to begin.
9.3 Mowing
9.3.1 Responsibility for mowing
9.3.1.1 All mowings which are carried out before the match shall be the sole responsibility of the Ground Authority.
9.3.1.2 All subsequent mowings shall be carried out under the supervision of the umpires.
9.3.3 Timing of mowing
9.3.3.1 Mowing of the pitch on any day shall be completed not later than 30 minutes before the time scheduled or rescheduled for play to begin on that day, before any sweeping prior to rolling. If necessary, debris may be removed from the pitch before mowing, by hand, without sweeping. See 9.2.3.
9.3.3.2 Mowing of the outfield on any day shall be completed not later than 15 minutes before the time scheduled or rescheduled for play to begin on that day.
9.4 Watering the pitch
The pitch shall not be watered during the match.
13.4 The toss
The captains shall toss a coin for the choice of innings, on the field of play and in the presence of one or both of the umpires, not earlier than 30 minutes, nor later than 15 minutes before the scheduled or any rescheduled time for the start of play. Note, however, the provisions of Law 1.3 (Captain).