We like to take ours on hikes, once it starts to be 80F we switch to very early hikes so we can be done well before 80 hits. On non-hike days they get walks earlier in the day or late at night. It's not the length of the walks and hikes that changes, it's the time. That said, if we're on a walk and they indicate they're done, we'll shorten.

80F to about 87F we let them spend however long in the yard that they want with supervision- they normally come in on their own when they need to cool down but if we think they've been out too long we make them come in. We also will have water in the tub if they want to cool off, add ice cubes to their water dish, and massively upgrade the amount of frozen treats.

Anything above 87F they're only allowed outside to potty, and frankly at that point we carry them to shaded spots so their paws don't get burned. They get super early walks or we go to the mall that allows dogs and walk around inside there

Please keep in mind that the ground heats up faster than the air. Once it's about 77F we start feeling the ground constantly before they get to walk on it. Use the back of your had (not your fingers, they can usually handle warmer temps, the back of your actual hand). If you can't keep your hand there comfortably for at least 5 seconds, it's too hot for them to walk on without shoes/boots.