It's not the neuter form--it's the adverb form, which takes a -t on the end like the neuter form. Think of it as the -ly at the end of many English adverbs (like quickly).
I read on a different thread that fort is to do with duration and snabbt is to do with speed?
It can be that way - much like you'd typically say "how quickly can you do this" but "how fast can you run" in English. But in this case, they're perfectly synonymous.