Karen - you are probably ok, then just do the lambs with the normal starter dose as soon as possible. It says on the bottle, I think it's four weeks? But not sure, haven't got one atm.
Dyedintthewool - you could always get a tup lamb, use him, and then eat in late winter/early spring. I wouldn't have the tup running with the ewes all year, but then mine have horns and I like them out of the way once I know the ewes are in lamb (too much pushing with horns when feeding time...). Or somene else near you with similar problem, but maybe an extra field? I have also had my tup on a summer holiday last year, sharing with two horses. They got on fine, as long as you know that the horses (and the tup and wether(s) too) are fairly placid and the fences are in order (Often not the case with horses....)