When breaking in a Mercury 4 stroke the manual says to vary rpms and stay under 4500 rpm for 2 hours, except running WOT for 1 minute out of every 10 minutes. It doesn’t specify if this has to be done all at once or if it is cumulative over 2 or 3 trips to the lake. What do you all think?

You don't have to do it all at once, but that dose make it nice.

Just keep up with your time and run it per manual. 

Thanks for the quick response!