if I understand it, the compression just kicks in right away, instead of after 3 millisec or whatever. and then if the release were at a low setting, the compression would end sooner.
ReaComp acts like most compressors in this respect. This is a great resource well worth a bookmark, Lot's of mixing/recording tips and specific uses of compression etc. HTH :)
After some tests I've made, the ReaComp seems to act like a faster compressor, acting in about 5 microseconds... I just wanna to some dev to confirmate that... please... :]