Diffenbachia are quite tropical, so you will have to wait until there is sustained mild, not just the end of cold. Minimums should be in mid 50's to 60's range.
Yes, they can endure temps into the low 100's outside, but in the shade. When it gets this hot, I also mist down the shade-growing tropicals a couple of times a day with garden hose. This will reduce the temps a bit.

P.S., Nice cat.

My dieffs grow outside without any problems in those sorts of temperatures. As Njoasis says, just keep up the moisture/humidity as much as possible.

I saw Diffs growing outside, wild in an empty lot, in full sun for about half the day in Costa Rica a few years ago. It was April, the daily temps were 105-110 f every day. It did rain for an hour or two every day I was there (A week) They were in great shape, showed no sign of sun or heat damage.

Yours should do fine in the conditions you've described. Just water them a lot once the heat hits town.

Mine are already outside. As long as it doesn't freeze, they tolerate overnight lows at any temperature above freezing just fine.

I have lots of houseplants growing outside. They stay outside unless threat of frost or freeze.