The tank will need about all of those 4 days to completely cure, so you aren't losing more than about a day.
I usually let epoxy cure for 7-10 days based on temp. and humidity. I also sweat it in for a good hour or so after mixing the two parts, again, based on temp. and humidity.
For a tank:
After the cure, water goes in for a couple weeks to try and saturate the coating, also to leach out some of the chemicals that come to the surface. Then I drain it and wash the surface with plain old Ivory dish soap. Rinse it out and do a fingernail test.
Properly applied and cured. Epoxy is a non toxic, thin film barrier that is totally safe for fish, if you do it correct.
You know things are in your favor if you can rub your fingernail against it and end up with a manicure
