That's a good question...i've seen first hand the damage that results from taxing over one, but i don't know how long they last.
As for attacking ships it's not unheard of for Blenheim's to go skip-bombing, check this picture from the wikipedia article:
Generally speaking, the RAF was a bit more "free-form" in its bomber tactics than the usual level bombing in formation thing that the LW and USAF had going for the most part (probably due to their weaker defensive armament) so don't be afraid to use their slightly unconventional but still historical tactics.
I've read accounts of diving attacks by Hampdens in night raids, bombers navigating almost solo to the target, pilots having a choice on their take-off time (within a reasonable timeframe of course), etc...it all points to the fact that they were trying to spread the bombers out and make them harder to detect, then they would try to hit the target the best way they could and if a formation is not an issue, dive bombing is perfectly valid.
After all, it does have a ring-and-bead gunsight available. Proper detonator and bomb delay selection to avoid blowing yourself up is another matter though
