It depends a bit on the kind of information that you can use. I prefer to use events to trigger methods and only use time-based triggers as an alternative.
If you have a buffer that contains the entire number of 43 parts, then you can use an entrance control to look if the buffer is empty each time you move an MU onto your container. Something like: if @.PreviousLocation.empty then @.location.move; end;
But this is only a first suggestion. If you share a bit more information on your own ideas (maybe upload a model) then we can offer more specific help.