I second going to group. I cannot do it alone. I tried...and failed, and gained a lot of the weight back. I need the accountability of standing on someone else's scales each week. I also like the social side of it (I'm on the social team - the people who help with weigh/pay and the shop).
As for how long the group lasts, it's between an hour and 90 minutes.
The first half hour of the time is for the new member talk, and for existing members to go through the pay and weigh stations. The "group" bit of the session - called IMAGE Therapy - lasts for about an hour.
So if the group start time is (say) 9.30, on your first week, turn up in good time for that. The leader will run through the plan with you and any other new members (or existing members who would like a refresher). Then at 10-ish, you'll move into the horseshoe of chairs, the leader will give you any news (such as new Healthy Extras, or forthcoming offers or special deals or whatever), then they'll give out any awards that people have won (for each half stone you lose, you get a sticker and a sticky-foot certificate), then they'll go round the group discussing how people have done and what they plan to do going forward. Then, at the end, the Slimmer of the Week (the person who has lost the most weight that week, who also had a loss or maintain the week before) gets the basket of goodies - every week, you need to take a piece of fruit or similar for them to win and the raffle will be drawn. The first week, you'll weigh after this.
In subsequent weeks, as long as you turn up before 10 am you'll be weighed - you don't need to get there for 9.30 unless you want to.