How long to give the "ditherer"?

[Horse]

My cars have daylight running lights.

If the other driver hasn't seen you out there (and the action of moving hasn't attracted their attention), then DRLs obscuring indicators is the least of your concerns

[sussex2]

If there is a possibility of a third party becoming involved then the decision is complex and has to be based on the likely actions of other road users.
The 'ditherer' in this situation is a third party and they can become involved; risk factors are increased dramatically and would need to be thought about carefully.
At situations with less risk eg someone who has priority hesitating at a mini roundabout my answer would be simple. If it is clear go. The situation described doesn't fall into that category.

[sussex2]

My thoughts:

1. None, no time at all - you should be in control of the situation not wasting time wondering if others are going to spoil your original plan.
2. That's not to say that the other vehicle isn't part of the plan. My choice would to be a tad (and I mean a tad) leisurely about getting out for the view so that the other driver has time to appreciate the movement. In general, I find (and FWIW for those who don't know, I work at one end of the road JonT is describing) that if they're going to go, they'll move out once they see you out there if they have any intention of doing so.
3. How 'buried' was the second vehicle? If they're so close that they can't see that it's safe to move out and they haven't seen you move out, then they aren't coming out.
4. I'd consider the need for a warning based on the body language of the car. Just giving one because of the manoeuvre seems pointless - it's like fitting a prophylactic to a marital aid. It might make you feel better but it isn't increasing the safety.

'it's like fitting a prophylactic to a marital aid' - Indeed if there are only two involved I can see your point but in the example given there are three and that increases the risk and the need for extra care

[martine]

I never thought I'd get relationship guidance from Stressed Dave...

[sussex2]

His attitude to safe sex seems a bit wayward

[TripleS]

His attitude to safe sex seems a bit wayward

To hell with safety. Any sex at all becomes a concern when you're a clapped out old buffer.

Best wishes all,
Dave.

[7db]

His attitude to safe sex seems a bit wayward

Out. Pause. Check. Go.

[TripleS]

His attitude to safe sex seems a bit wayward

Out. Pause. Check. Go.

Shouldn't the check come before you go in, never mind about out?

Are we getting slightly OT here?

[TheInsanity1234]

You're all doing it wrong.
It's
In. Out. In. Out. Shake it all about!

[skodatezzer]

And I thought this was a respectable forum!!

[TheInsanity1234]

Nurse!
The men are getting randy again!

[cupraray]

anything could out accelerate an alfa jts

[cupraray]

His attitude to safe sex seems a bit wayward

To hell with safety. Any sex at all becomes a concern when you're a clapped out old buffer.

Best wishes all,
Dave.

the bucket method is best

[TripleS]

His attitude to safe sex seems a bit wayward

To hell with safety. Any sex at all becomes a concern when you're a clapped out old buffer.

Best wishes all,
Dave.

the bucket method is best

Well now, being relatively innocent (and ignorant) of these matters, I eagerly await enlightenment. A PM might be prudent.

[TheInsanity1234]

His attitude to safe sex seems a bit wayward

To hell with safety. Any sex at all becomes a concern when you're a clapped out old buffer.

Best wishes all,
Dave.

the bucket method is best

I hope you're not referring to the 2-bucket method used to wash cars?!