Welcome to Arizona. Citrus and hibiscus like to be fed when the weather is warm and they are in active growth. For citrus in the ground, I use citrus fertilizer on Valentine's Day, Labor Day, and Memorial Day (that's sort of the classic routine in the Valley). It's strong stuff though and I find it burns plants in pots, so for my few potted citrus I use general purpose Miracle-Grow dissolved in water according to package directions. For the potted plants I fertilize them with Miracle grow once or twice a month, April through August.

I'm not growing hibiscus in this garden, but I have in the past, and I had great luck with all purpose fertilizer (bloom booster type is good in summer) during the warm months. If their leaves get yellow with dark veins they aren't getting enough iron because of high pH so you can either adjust your soil's pH or just use acid-loving food on their roots and foliage a few times ("rhododendron/azalea/camellia" fertilizer).

They're both pretty easy to keep happy--just fertilize when it's warm to hot, and don't give them much fertilizer in autumn so their growth slows down/toughens up for winter. I'm sure lots of our members have similar, or totally different, regimes that work for them too. :)

Good luck and keep us updated,
Grant