Awww, that's nothin'! It can get over 100 here for days in a row, with a "break in the heat" being a dip down to 95 or so. This goes on for 3-4 months, with a long stretch of high 80's / mid 90's book-ending on both sides of the really hot part of summer. I wouldn't worry about those fluctuations from night to day, or day to day, that's natural. All of my plants are fine with it, except Fuchsia, but I don't think you have one of those anyway. Everything else grows like crazy in the summer. Nothing gets much sun from about noon-1:30, except Sans. Everything is placed to get either morning sun before that, or afternoon sun (a lot hotter, especially for roots in a dark pot.) When in doubt, go with morning if you have the option there. Back it up a bit if you see some sunburn. My plants have been outside since mid-March. Once they go out, they don't come back in except in the case of frost which, if I've decided correctly on which day to do this, won't be until winter. The weaker the sun rays are when they get out there, the easier it is for them to adjust to much more sun, gradually as its' angle changes. I know that's way too early there, but just wanted you to have the info for reference, confidence. And I know you're the type to take them in & out, very useful in Z4. Look how lucky we are, supposed to be cooler all week until the weekend! We've almost hit 100 here a couple times already. If you click the blue "monthly" at the left, check out the end of last month.

Where are you measuring the temperature? Amoungst the plants or at the top of the roof?

Yep, been there, done that. A year or so ago my heat mat thermostat gave up the ghost. I figured it was 10 - 12 hours before I caught it. My tray medium was in the 135F range. My tray had been seeded two weeks earlier so I had sprouts in a number of cells as well as a number of un-sprouted cells. I killed the heat until I got a new thermostat. All my sprouts made it and a number of previously un-sprouted seeds as well. I'll never know what my germination rate would have been if... Given that you're only 3 days in, if you don't want to take a chance and have extra seed, re-seed your cells. If you're short on seed, roll the dice. You should get something. Just my humble opinion. Bill

In my experience, everything elastic does OK on "warm"...by which I mean 100F or so. When I want something white really dazzling, I'll select Duet's "whitest whites" setting which boosts to 127F. However, 127 begins to take a toll on elastic with repeated washings. I've seen this in my underwear and the corners of my bottom fitted sheets. You'll see it beginning after your first experience. Strongly suspect "sanitary" cycle which boosts to 155F would hurry the deterioration but haven't done it repeatedly so don't know.