Jim, The Bondo brand Spot & Glaze putty you show here does not use a hardner. It will set in minutes right out of the tube if used as intended, thin coats.
I use the same putty, it does require a hardener, as it is a 2 part putty. There is a single part putty made by Bondo, that is in a similar tube.
You do learn something here every day. I have been using Spot & Glaze putty on models and real cars for 40 years and never saw a two part type.
The tube I have looks like that tube, but not sure about the "Professional" name. That said, it's probably 10+ years old. Mine is red and dries in minutes. I like it because you don't have to mix it and it dries quick.