It depends on how many people are receiving the Eucharist and the number of priests and EMHCs distributing. Most of the time, where I attend mass and at other places I’ve attended, they get through one hymn. If the line is much longer than expected, the organist will play softly, either improvisation or a composed instrumental piece.
When there are special masses such as during the holy days, feast days, etc., the music director/organist/etc. will usually plan more than one hymn - sometimes 2 or 3.