So how long did a typical huge army vs army battle take in Medieval and Ancient times. And What was the longest recorded battle In those times. Not including a siege. I mean head on.
This question was answered very well in this thread. TLDR - Usually about 3-9 hours, and sometimes with multiple engagements over the course of days.
The thread also discusses the 1683 battle of Vienna, which lasted 20 hours straight. Though there is some debate about whether that is a "medieval" battle. Outside the time period, but fought using antiquated tactics and pre-firearm troop types.