I take mine out daily from day 1 too, but it is 90+ degrees here, and if anything, I worry about them getting overheated. Still, when I am raising ducklings in early Spring, I still take them out daily. I have a shoplight that I set up nearby that puts out a lot of heat, and they huddle up close to it when they get chilly. When most of them are huddling, I know it's time to head inside.
But, mind you, I also supervise them every second until they get a little older. Once they're a couple weeks old, I make a small temporary pen out of wire or whatever I have around to protect them from wandering dogs & hawks and so on, and then they can be outside without me as long as I'm home and can check on them periodically. Tomorrow, I should be getting a (used) large wire dog crate with a removable bottom pan, so I can just set it on the grass (with the bottom out so they can be right on the grass), put water and food inside, and let them stay out there even without me (they will be two weeks old Sunday). Of course, with the heat here, I make sure they have water to play in (no more than an inch or two) and lots of shade.
This is a side topic, but I was surprised this time around that after just a few days, the ducklings stopped using the brooder light altogether. I don't even have it on now, because they were spending all their time on the opposite side, and avoiding the light completely. With previous batches, it seems like they used the light for weeks. Is this the difference between home-hatched ducklings and those that spend two days in a shipping carton? Or is it the difference in the time of year (these are my first summer ducklings--but they're indoors, so the temp difference is only 10 degrees--which I guess is a lot...)?
Anyway, yes, feel free to give them supervised outings. Just watch for them to start acting cold.