They should be fine to go outside for a little while as long as you do it during the day while it's warm. They shouldn't need any grit b/c they'll be able to pick up some sand/dirt while they peck around.
I agree, to a point. The OP said it's "typically breezy", the breeze concerns me more than the temps.
To the OP - If you do it, try to pick a day when the wind is calm. You'll have to watch over them like the mama hen would. If they are moving around, making quiet peeping noises, then they're fine. If they start to huddle and begin to peep loudly, it means they are chilled and need to go back under their heat lamp.
I don't believe in keeping chicks under their heat lamp for an extended period of time. Mama hen has them out from day one, always ready to take them back under her ultra-warm wings and body if they show signs of chilling. Just MHO.
I agree with gritsar. When the babies get cold, they go looking for shelter. If you're out there with them, you'll know when to bring them in, just like the mama hen does. In my experience/observation, the mamas take their clues from the chicks as far as when the chicks need some warmth.
With all due respect to the guidelines for temperature, i have pretty much decided to ignore them. My chicks have never conformed to those rules at all. I just make sure my babies can get as warm as they want to when they want to.