Well yes and no...
See weekend blocks aren't very nutritious and, as they dissolve, the release minerals into the water that can alter pH and hardness. This can cause more harm than good as a sudden change in pH can kill your fish.
On the other hand, if you feed your fish several times a day daily and stick to this routine invariably, a sudden change could also be detrimental. If you plan to go away for any amount of time, you should skip a few days of feeding, gradualy increasing the length of time, beforehand.
Having said that, a couple of days shouldn't kill any healthy adult fish. As fish are cold-blooded animals, their metabolism works very differently to ours and they can last without food longer.
If you could feed only once and not too much on the wednesday before and skip a day of feeding the thursday but then feed quite well on friday evening, the fish should last the weekend.
However, if any of the fish show signs of having internal parasites or a hollowed-out belly, you will have to make sure they get fed over the weekend and a block will be necessary.
Something else you may want to consider is lowering the temp (only slightly and gradualy) to slow their metabolism while you are away or to buy an automatic feeder which will feed quite reliably for longer (if you ever decide to go away for some more time). If there are plants and algae in your tank, your fish can nibble on these too and that should sustain them for some extra time if necessary (it wont be for just 2 days though).
If you can get someone else to feed, that's always the best solution - but your fish should be fine for a weekend without food.
