I'm not sure about when to fertilize because I'm so bad about fertilizing any of my plants. Ixora do prefer acid soil and spring would probably be a good time to begin feeding lightly. Use a plant food/fertilizer specifically for acid loving plants like azaleas and gardenia. I'd start with 1/4 to 1/2 the strength that's listed on the label.
If the plant has been in your basement all winter, gradually move it to a sunny spot. Ixora are landscape plants grown in full sun here in Florida; they will bloom in bright shade but produce more profuse blooms when grown in full sun.
~ I'm an old gal who still loves playing in the dirt!
~ Playing in the dirt is my therapy ... and I'm in therapy a lot!