If the label says twice a year that means every 6 months, you can feed half the dose every 3 months or 1/4 the dose every 1 1/2 months. That's up to you. Citrus likes to be fed quite so often and should show on their green leaves .
Also if you only have 1 lemon, why don't you use a fine net around your tree until those crickets get so hungry they'll fly away to find another victim or fine wire mess at Home Depot or Orchard. Won't be that expensive. You can remove the net after sometime.

As an afterthought is your citrus fertilizer contains the trace elements? If not get rid of it and buy one that contais the Trace Elements. be sure it also contains the trace mineral zinc along with Mn, Fe and Mg. Zinc is an importrtant trace mineral for citrus.
Also have you flushed your pot soil lately? If not your soil may have built up salts that are toxic to your plants.
To flush your soil, take the pot outside and put your water hose to your pot and run the water perhaps 15-30 minutes in slow run making sure no soil goes on top and spill out. You should do this about 3 times a year.
Once you do this you'll see a new plant that just had a new bath perky and perhaps new growth. The greening of leaves will come later.

That's a great idea - thank you! I'll go to the nursery today and ask about some fine netting.
I had already re-potted her *before* reading this forum. The owner of the nursery told me I could use just potting mix - I mixed 3/4 potting mix and 1/4 good quality organic compost...no coconut husks - should I be rushing to amend what I did last night? - Roberta

No Roberta. If you can add some sand if not too heavy for you mix with osmocote fertilizer I think 17 4 12 or just regular steer manure would be just fine. look at the recommended dose. Add 1/3 of each sand potting mix and organic compost and a spade of steer manure or osmocote.