So I took the plunge and made an Imperial Psyker, and to ward off/prevent the summary bullet to the brainpan I decided taking Preternatural Awareness would be a good choice. I'd like to know how some of you game masters out there rule on using this (very valuable) power.

To wit: If I want to benefit from the additional initiative bonuses, do I have to maintain the power throughout the fight? (To me, it seems as though I would have to), or do you allow it to be used up until the point of rolling for initiative, then the power can be dropped?

If you say "use throughout the fight", then does the initiative bonus fall off if the power is dropped once fighting starts? (i.e. JoeBob the IP uses PA, initiative rolls are made, JoeBob maintains power for 1st round, allowing him to add WP to initiative, then on the second round, drops the power, losing the WP bonus to his initiative)