For 3bld , the memo can consume 30-50% of the total time , since you can use audio to speed up.
For bigBLD, it is good to have a consolidated memo , so I agree with Mike Hughey and try and maintain a 50/50 split.
For MBLD, it depends on how much you are pushing, for a beginner in MBLD who is doing 6+ cubes in MBLD, having a memo of 30-38 minutes work the best, although there are exceptions.
But 30-38 minutes is the sweet spot for memo in MBLD even if you know 3-style or you do not know 3-style.
Once, you start becoming familiar with MBLD, having 40+ minutes of memo will be good, since we can maintain the pressure during execution , and have less pauses, and more 3-style turning.
By the sub-X format , memo splits:
for 3bld
sub-60 seconds : 25-35 seconds (assuming M2/OP)
sub-40 : 20 seconds (Assuming advanced M2 and some 3 cycles )
sub - 30 : 10-12 seconds (Assuming 3-style)