How does high skill reduce a spells casting time?
To figure the reduced casting time of a spell known at very high levels, halve the casting time and round up at each stage (i.e., at skill 21, 25, 30, etc.). Do not just raise 1/2 to some power and multiply, then round up. The exception to the rounding rule is when halving takes the casting time below 1; then you round down to 0.
