If you do, let it say, 1 hour show, and you are getting hired for a customer that want you to do the performance in two parts, here are the questions:

do you just break the performance in two parts?, or

do you have to look for two diferent openings, and two diferent closings to do a two little routines?

Just a thought -- end the first half with an effect half completed -- a mystery shared without resolution and no obvios result. Then you can start the second hald with the resolution and magic -- possibly a completley unanticipated result.

If the audience is the same for both parts then the second can be a continuation of the first; If it is a different audience then you should treat them as separate performances with each having and opening and closing.

Hopefully sometime in the first set you have established your personality with the audience and won't have to re-do that, but in the interest of good theatrics if it were me I would definitely have an opener and closer for each of the sets.

yes, most of the audience is the same, I am working in a night club, they have a music band, then the magician, and again the band.

But now the owner wanna do it -band-magician-band-magician-band-
does anybody here have the same situation?

It sounds like a good situation and you should leave the audience wanting more after each "segment" so they don't wish for the band to hurry back.