Sounds like your GPU (video adapter) is overheating and it takes a moment to get it down to a "safe" temperature. Does this happen all of the time, or only when pushing the system hard (like when gaming)?
You can try using an app like SpeedFan (just google it) to adjust your fan speeds/settings. You can also take a can of compressed air and blow out the dust that accumulates in systems. Power the system down and then blow air into both the intake and exhaust ports.
Thanks. Unfortunately Acer laptops seem not to expose many of the handles that SpeedFan wants to use. I see temperatures (83+) but all fan speeds say 0 and no adjustment of fan speed controls make any audible difference. No parameters are exposed for the graphics (3850). Thanks for the suggestion anyway.