Change in dose, how long to see impact?

[LLS8000]

Sam, my 14 year old miniature poodle, was diagnosed with diabetes on 5/12, started injections on 5/14. It's been going well, but it does seem that injections are becoming more difficult, but certainly manageable. Tonight, he ate all of his food, he's always starving. Then I gave him his insulin dose, which seemed to go fine. About an hour later, I let him out in the back yard. He was out in the heat (low 90's and humid) for about 30 minutes, and started stumbling. Husband grabbed him, and I grabbed the Karo syrup. We got him into the house, with the AC on. He licked up the syrup, and I gave him a few organix treats. He seemed better fairly quickly. I'm glad I was home, and noticed the stumbling pretty much right away, this is our first hypo episode. We're early on in the regulation stage, and the vet is taking him on Friday to do official curves. He seemed to be doing so well.
I'm sure it could be many things at this point, but does anyone else notice heat having an impact on your pet? That's the only thing that I can point to that was different tonight.
Still keeping an eye on him tonight. Thanks.