as in about this whole world-on about any line, there are busy and not so busy days. NOOne will ever be able to give a full answer on that.
But if you find that train is full (wich as such is rare, but can happen)-there are scores of 2nd hand and older buses doing the same run-much quikcer, much less comfy and for prices like 15-20€ (note that MOL is out of any IR-area so you always have to pay the extremely low fares in that country)
OR: take nightrain to IASI-still in ROM, get out next morning, open eyes, find some brekkie, and then find the minibus to CHis-many/day-drivers will solicit custom on station. Or-even cheaper-citybus to Border (nicolina)< cross over, then find (have MOLD lei=other as ROM lei ready) a local bus to Chjis-ev 15/20 mins.