I haven't tried it, but there is now a 20 wave horde option for custom games. Wasn't the classic horde event 20 waves?
All this timed horde events are 20 waves, but in custom games you can't change the ruleset of horde besides the modifiers.
Classic horde was a mode where there are no classes, fabricators and all that stuff from modern gears, so is an different ruleset than the current mode. And is the same with Jingle Juvies