No, I don't think feeding while they are dormant will make any difference. March is probably the best time to give them a helping hand . . .

The compost mulch seems a good idea though leaf mould would be better. A little balanced fertiliser fortnightly & keep pots moist until flower buds appear then switch to a high potash feed.

Agree with Sheila, don't fertilize anything now, its the wrong time of year, everything's preparing itself for winter and going into dormancy, and there's a small amount of balanced fertilizer in the new potting soil you used anyway. A handful of Growmore in spring will suffice, or whatever balanced feed you have available, although if the leaves are plentiful and healthy at that stage, use a high potash feed diluted to half strength once flowerbuds start forming. If you can be bothered, I usually don't notice the buds anyway so by the time the flowers are out and I do notice, its already a bit late for potash! Its really not essential in the ground, they flower regardless, but in pots its probably a good idea - you might be interested to read this

http://www.cathsgardenplants.co.uk/Tips---Advice/Growing-Barnhaven-primroses-or-primulas.aspx

next year consider doing the general feed in late summer/early autumn especially f you want flowers through the milder bits of winter.
But as for now its not really the right time of year. if you can guarantee warm weather for the next month then a small amount would be ok but as we cant I wouldn't waste your money. also excess 'feed' can cause the plant to lose water and other minerals.

Thanks Bamboo - and that's a brilliant link - tells you all you need to know :)

Thanks Bamboo.