My Samson LOVES to sunbath. In the summer time it gets HOT where I live. So when it's 100's, 90's and 80's out, it's outside to potty and I make him come STRAIGHT back inside. 70's is a judgement call, if Samson starts getting all pink and panting while he's sunbathing I make him come inside. Personally if it's just in the 60's/low 70's I let Samson stay outside as long as he wants. Same with walks, I wouldn't walk Samson for very long (more than 10-15 min) if it's over 70.
As for adequate exercise in hot times. I get a toy Samson loves and find a place in my house where I can throw it and its a long stretch for him to run and get it. So I make him play fetch like that just in an air conditioned house, that always works to get him nice and tired Hope that all helps. SOOO glad to hear you are adopting, there are so many bullys that need homes so I'm always so happy to hear when someone has opted to adopt.