Alan, either you are desparate, or you are paying me a great compliment by posing your question here.
In my part of the world, citrus fruit can only be produced under glass, with artificial heat. Ergo, I am no expert.
However, I don't think timing of pruning is an issue. If it needs pruning, any time is better than never.
Firstly, relieve congestion and assist airflow by removing any crossing branches. No branch should rub against another.
Secondly, I believe the lemon is spur-fruiting, so cut back leading shoots by at least a third, to promote spur growth (side-shoots).
However, as I say, I am no expert. But the basic principles of pruning fruit are the same anywhere. Don't let them become congested. Keep an open tree, and cut back leading growth to promote spurs.
Best I can do, I'm afraid.