If you put the compost in there, it will have a couple of months to percolate in the soil, but you will lose any extra growth by the clover. If you put it in now, it is clear to me that you should cut it. If you wait until May, you will have twice as much clover biomass, but the compost will not be as well blended in the soil as it could be. Given that you have already some N in there from the current clover, and that nutrient availability is crucial with toms, I vote cover and cut now.

I would clip the clover tops as close to soil level as you can. Put the clippings in your compost pile or use them elsewhere as mulch.

Then add your compost or compost/soil mix to top off the bed. If you're adding any organic fertilizer (seed meal, bone meal, kelp meal, etc), stir it into the top couple of inches of your new topping.

There is no advantage to letting the clover flower or go to seed. Clipping the tops now, the existing roots will start decomposing, adding nutrients and opening channels in the soil for the tomato plant expanding roots.

IMO, if you wanted to keep the weeds down and help to decompose the clover roots, cover the bed with flattened cardboard and some rocks or bricks. This will help to prevent nutrients from washing out between now and when you plant your tomatoes. The earthworms and other soil fauna will be working under the cardboard.

Sue