Unless there is a strong nectar flow (field nearby with oil seed rape for example) and good weather I would give them gallon or so of 50:50 sugar syrup. It will do no harm and only good. To be extra careful you might want to delay feeding for say 48 hours, this gives them the time to empty their crops and it reduces the chances of disease. Like starving a case of "the runs" although if there is a nectar flow on this won't work.
If you want to really kick the varroa - and they will have varroa unless they have come from somewhere varroa free, you could treat with an OA trickle or give them 20 mls of 60% formic acid on a J cloth over the top bars. Probably best to put the QX under the brood box while doing this. Have the varroa tray in and you will see how many mites fall. The formic acid treatment can be repeated after a few days but only do the OA once.