This depends on the temperature of your working conditions and how much catalyst has been incorporated into the mix. Warmer temperatures will reduce your curing time and colder temperatures will increase the length of cure.
Likewise, adding extra catalyst will speed up the curing process - often necessary for colder temperatures and reducing catalyst will reduce curing - again often necessary during warmer temperatures.
We would recommend mixing no more than 1.5 - 2kg at a time. Once the resin and catalyst are mixed, the curing process will begin and you are working against the clock to get the resin applied - usually no more than 20 minutes. Only mix as much as you need.
Epoxy Resin is mixed on a ratio basis and should not be altered.
Room temperature is the ideal scenario for curing. Each resin type will differ so we would always recommend referring to the MSDS and TDS available on each product listing before use.
Although some resins may be hard to the touch after 24 hours, some may not be fully cured for up to 3 days. Again, this information will be available on the product Technical Data Sheet (TDS).