For me it could be several hours, sometimes a day or so. It depends on how low and if I overcompensated and went high or not.
Have you considered adjusting your basal rate prior (up to 2 hours) to your exercise? How about a snack before and/or during?
It might take a few days to get a handle on the routine change. I know it does for me.
I suffer from AIH, Amiodarone-Induced Hypothyroidism (currently in the monitoring stage, without treatment), so I'm easily (continually) fatigued. Plus I'm on a handful of other medications so much of the time I'm trying to decipher which condition/side-effect is responsible for the varying symptoms.
And to think my wife was concerned how I would occupy my time (and my brain) when the grand kids started school this year. :-)
I'm a 'stay at home' grandfather to a 3, 4 and 5 year old - talk about exhausting!