[dsraven]

lots of guys use something called dry guide coat powder. just google it.
if the epoxy sits longer than the 24 hr time then you will need to scuff it up before putting filler on. the chemical bond between the not cured epoxy and the new filler wont be the same as it would within that 24 hrs. check with the brand of epoxy but I'm pretty sure a month later means sanding before filler. if done within the time linits it's kinda like putting another coat of paint on, it will chemically bond.
the lpywood board sanding block is my go to. a hard office eraser works for small curved areas. a wooden dowl works for bigger curves. crosshatch pattern for sanding ensures you don't make flat spots with the sander.