At least 3 to 4 months. I have had field Meyers hang as long as 10 months in trials before starting to lose juice and fall from the tree.

All gardening is local. I recommend that you experiment with how long they will hold in your area. I usually leave some holding year round. I begin by thinning out the larger clusters, taking the ripened ones first and leaving the greener ones to hold longer.

Thanks!
Though Meyer is not my preferred lemon regarding flavour, it must be recognized that it is an excellent variety, very productive, early ripening, nice looking, easy for growing (at least for me) and, good hanging on tree.
A must have variety!