In fact, we all left at 19:45, with 15 minutes of the period left.
(No, we didn't get there till 18:00, so our contribution was a bit under 2 hours. Evening sessions will be like that though: not everyone gets off work at the same time.)
There seems to be a point with fencing where suddenly it becomes much quicker. It's somewhere around the point where a whole length of chicken wire is being held up against the posts: if there are two people left over to staple the top, that bit goes twice as quick as if there's only one.
