DND_Reborn
The High Aldwin
I think 5-6 rounds is about par for a Deadly encounter. However, I can't imagine either of these combats taking more than 30 minutes from rolling initiative to the last opponent falling.
Honestly, I still can't conceive of a combat taking 4 hours unless something really strange was going on like a dynamically shifting environment.
I know that you run a lot of house rules based on your posts to other threads. What house rules are you using? Are you using Greyhawk Initiative, weapon speed, flanking or some other house rule that might add to the administrative overhead of the combat? Are you using miniatures or theater of the mind? How experienced are you and your players? Are you playing in person at a table or are you on like Roll20? Are you using any digital tools as DM? Are you flipping around the monster manual or do have a way to have all the monster listings at your fingertips? Do you have children or the television on or lots of texting or other frequent interruptions/distractions during play? Are your players descriptive, or do they just say, "I attack the guy in front of me again!" and roll a die?
Actually, most of the house-rules our tables uses speeds UP combat. We only roll once for Initiative, and the DM uses an excel spreadsheet to put in the numbers and it has a macro that auto-sorts the list. It is on the wall mounted TV so everyone can see the list and knows their place in Initiative.
Our DM never rolls damage for monsters, just using the averages, and crits deal max damage. Players (such as myself) can also do this. Most of the players still roll damage though.
About 75% of the time is theater of mind. We have a battle map and use dice/minis for major battles sometimes, but other times we even use theater of mind for those.
Flanking is advantage per RAW, determined by the battle map if used or by DM discretion for theater of mind.
The DM and myself are the most experienced (decades for each of us). The other three are all sort-of new. Two have been around about 13 months, the newest only 5 months.
The DM has everything on his laptops (he uses two, one for the game and one for reference), but has monster stats directly on his spreadsheet where he tracks everything else. He showed me how it works and it is pretty cool IMO. He just types in the damage when a monster takes it, and the current HP cell updates instantly.
For one of the players, a cell phone is a distraction at times. We've talked to him about it and told him if it doesn't get better he'll have to leave it on the back table.
Play is normally "I cast fireball at them." or "I attack the closest wolf." etc.
Some of the players have spell casts to hep them in referencing their spells, to that helps.