For a party it's probably just best to play it by ear rather than run a strict timeline.
For pub \ club and function work it's not the band who decide on how long but generally who's paying the money. I've been fined while working in a duo for cutting 10 mins off a set before and a favorite trick of landlords is to dim the lights when they think you should start as a gentle hint The big clubs want to get their moneys worth as well, normally at least 3 x 45 min sets.
My band usually do 2 and a half hours, no breaks. my drummer pushes for more sometimes but I' actually hoping to reduce it to no longer then 2.
as for the no breaks policy, well we all decided that one needs breaks, there are songs which we all dont play, we can simply que two together if one person need to change a string/take a breather/get a drink/use the bathroom.
I know having a break is compleatly normal and that you can't exactly go for a piss whenever you want if your playing drums at an ACDC tribute night, but when the genre allows it,(jazz, rock'n'roll, swing, blues etc) I love watching bands that can carry on while members take care of their little problems and have quick breaks.
Thanks for all the suggestions & comments. To draw a line under everything I would offer the following comments:
1) Quite a few of the people attending are mates who haven't seen me play for 15-20 years. Some of the songs are ones I used to play then & they have asked to be played again.
2) A large number of guests are family, most of whom have never heard me play, & some of whom will be getting up on stage to sing & play.
3) It's my party so I'll play for as long as I like!!
And there will be a 'disco' afterwards when I will mingle (and get drunk like the rest of them!)