Timing for row-throughs is in this spreadsheet
https://docs.google.com/spreadsheets/d/1Z_a0FutZ-VMqOo6u4gZi9MCjkgecXmNbOSYtMq3LIPg/edit?usp=sharing
There is a half-hour window for rowing through between divisions. If the racing is late for any reason, crews rowing through may be held at marshalling points. Crews which do not arrive to marshalling in time for the end of the row-through window may be held until the end of the next division.
No rowthroughs are required before 8.30am or after 3.00pm, but it helps to know about, if part of your outing requires a rowthrough.