Yep, you will be more sensitive to spikes being off basal for a few hours, so find numbers that make sense for you. Under 100 = 1 tab, or whatever you feel comfortable with.
But, do it right before you get in the pool, not when changing!
timing-of-pre-workout-carb-consumption
That way it is consistent. Because inevitably, walking from the locker room to the pool, old-lady Benson or old-man Jackson will strike up a conversation with you, delay you a few more minutes, and you will spike. And then you will be cursing them the whole time you are swimming. 