Why risk it, if every adhesive manufacturer says the same, then you gotta think there’s actually something in that guideline that is true.
Ie don’t fix below 5degrees.
Make the client add a couple of space heaters or something in the garage and raise the temp to an acceptable level.
I’m sure it wouldn’t take much, unless of course we’re talkin commercial size garage.
And even if you are, it’s far cheaper to safeguard than it is to replace.
That’s just my opinion tho, but I would insist on heaters if it was necessary to tile it now.
I really don’t get the idea of cutting corners to save 5% cost or whatever.
Replacing it costs 200% more, let alone initial outlay.