I give you an instance to consider. The Beach Bash event ends in about 20 hours. The Beach Brawl roadmap expires at the same time, in about 20 hours. Based on the timing of how this event ends, I don’t have a chance to spend my final beach balls, on a final Beach Brawl roadmap, which means I don’t get the chance to obtain the maximum number of umbrellas to trade in.
I think you should be able to run the final road map on an event and the collection milestones have completed and still have time left to make your collections or black market purchases.