I’m a newer DM who started a campaign 3 years ago during COVID with my brothers. Take my advice with a grain of salt because it may be different from others. My campaign is based around a group of characters that go from start to finish. My campaign revolves around some star wars fanfic I wrote back when I was too poor for college classes, yet knew my writing needed work. Thus, as a DM, I’m the one unwilling to allow player character death.
I am extremely lucky to have very mature players that mostly don’t try to cheese the game. I usually give them a time limit for a mission to be completed, either explicitly from the quest giver, or implicitly where “bad things” will start to happen the longer time goes on and the mission isn’t completed.
Could my players take more long rests? Absolutely, but that could cause them to fail that quest. Could my players take a long rest in the middle of the day right after waking up that morning? Absolutely, but they better have a plan for what they are going to be doing that night when all the shops are closed, it’s dark, and NPCs want to be left alone. And besides, it’s tough to fall asleep once your circadian rhythm is off… It would be a shame if characters needed to start rolling constitution checks to see if they can fall asleep to get that long rest for the next couple of days, and imposing exhaustion levels for not getting a long rest if it goes on long enough…
You’re NTA, but your friend is also NTA in my opinion. There is a lot of communication that needs to happen here and they also need to be able to trust that you’re not “trying to kill them”. You, as the DM are trying to tell their story in such a way that they feel epic, yet balance that by in-game consequences. It might be a good idea to try and sprinkle in some consequences for constantly resting, like the insomnia/circadian rhythm mentioned above, or maybe an ambush from bad guys that figure out the heroes location and prevent a long rest from happening. Forcing them to flee and hide after the ambush, wasting the rest of the day, might help them get moving. Those ambushes should be scary enough that they would go to great lengths to avoid a repeat.
And one final thought is to possibly think of your campaign like a movie. Yes, you’re telling their story, but you’re not telling every moment of their story. You’re not forcing their characters to stop for 3 meals a day, go to the bathroom, and occasionally wash their clothes and take baths. No, you’re hitting the important parts of the story, and filling the gaps with downtime where they can fabricate things, work “jobs”, etc,.
I hope something I’ve rambled about helps you out!