Perhaps the Lonseal 650 has a set range, but WEST System epoxy has a very wide range of temperatures it can be used in. It's used in boatyards all the time (cold/hot/cold-hot/rain/wind - we have it all!). If you are using the 105 resin, then you have a choice of hardeners. Fast hardener can be used down into the 40's. Slow can be used at temps above 60ºF and into the 90's. There is even an extra slow though I haven't used that one much.
There are "tricks of the trade" when using epoxy in hot weather:
1) Don't mix up a batch and then keep it in a deep cup or bucket. It "self heats" and kicks very quickly. Instead, spread it out right away. It will kick much slower then (in same temps). If a smaller batch, something like a lasagne pan works well. For a larger project, just dump it on the surface and spread it out roughly, then come back and spread it exactly how you want it. It kicks much slower spread out than in a typical bucket.
2) Keep the resin cool before mixing it. This is kind of "making your own weather" (within reason). Van is outside but you live in an air-conditioned house? Keep the epoxy inside until just before you use it.
3) Mix smaller batches. Have separate containers of resin and hardener (and any thickener) pre-measured and ready to go, then mix hardener and resin (then thickener) just when ready and you can keep a pretty steady job going whilst not letting the epoxy kick.
4) Some people even put the mixing cup in an ice bath, though I have not.
I have found that with a combination of #1 and #2 plus slow hardener, I can do even larger projects in hot weather (you can also mix smaller batches). Cold weather is much easier, just use fast hardener (though obviously the Lonseal itself probably doesn't want to be unrolled and installed in frigid weather).
Obviously 72ºF is the dream, but there are ways to mitigate warmer and cooler temps when using WEST epoxy.
WEST System has oodles of free publications and a great tech help line. Since boat work is often outside and in inclement weather of various types, they have seen it all.
Hardener selection determines epoxy's open time, cure speed, and time available to mix, apply, smooth, shape, assemble, and clamp your epoxy projects.
PS: 100% with you on the benefit of epoxy also sealing a plywood floor.