please help me Pwm Timing, RC Stuff

hi all
im fairly new to pic basic though so far it rocks, but ive managed to get stuck.
my problem is i want to be able to measure the duration of a pwm pulse then either hserout it or just make an anologe ouput signal to be a/d by another pic.

the problem is the speed and i dont know if i can even use a pic to time that accurately

its
a 46.7hz signal
with a 21.4ms off cycle

the pwm signal goes from

11.2us (0%)
to
20us (100%)

if anyones got any hints for this that would be awesome
thanks
eddy