What are the rules regarding exit and entry permits for a Non-O retirement visa in Thailand?

Hello,

I have a Non-o retirement visa.

I am hopefully going back to 🇬🇧 in late May.

I don’t know the exact date I will return, but it will be well before my visa expires.

1. Does the single exit and entry permit you buy from immigration have to be on exact dates?

2. Is it better to get a multi entry visa?

3. How long does it take to get an single entry & exit permit or multi entry visa?

Many thanks in advance 🙏