If your Meyer lemons trees are nice size, I would do no thinning Your tree will retain only the amount of fruit that the tree is capable of bring to maturity. If you do decide to thin the crop, I would wait until after the early drop period is over. For a Meyer lemon tree the natural progression is: flowering, original fruit set, early fruit drop, a little June drop, then fruit sizing and maturity period. There is no rush to do any thinning if you later on decide to remove some fruit.