There are a couple attributes that you can set via zmprov that limit the size of the redolog before it gets rolled over. Not very well documented, see
[SOLVED] Growing redo.log file
But I don't know how to force a rollover ad-hoc or at a specific point in time. Another attribute I just found via
zmprov | grep -i roll is zimbraRedoLogRolloverMinFileAge, but that sounds like it would do the opposite of what you're looking for.