i incorporated mulabhanda into my pranayama recently, but i was wondering how long you are to hold it. is it like with sambhavi wherein you hold the bandha constantly? i was in the habit of twitching the muscle whenever my attention was down on the perinuem as a way to reinforce the location of this elusive little patch of body :-) i thik i would find it difficult and distracting to have to hold it the whole time.
I agree with EMC, you will have to figure out, how long to stay in mulabandha, for yourself. The idea is not to force yourself to stay in that any position just stay with it for as long as you feel comfortable.
If holding on to mulabandha is distracting, you could try asvini mudra.
It might be a bit easier if you do the gentle flexing on the rising inhalation during spinal breathing and release it on the descending exhalation. Then the breath will be a cue for flexing. This is actually called asvini mudra, the alternating flexing and releasing.