Could be either way, in my opinion.
That said, there are some things which stand out.
"As this game is already one where you cannot really recuperate from a fight. As once the clock hits 12 we all wake up back at our camp regardless if were alive or not."
That sounds like a situation where death is a slap in the wrist. Maybe you can use this? When I read this it's like 'oh, that's why the guards are invincible, because there are no consequences to the players losing a fight with them. They don't seem to stay hostile between loops, too, hmm..'
There's a lot of information that I'd like to know here. Is it a proper groundhog's day loop where everything is reset, or is it just the party? If so, what happens if you, say, wreck a building? Can you set up a decoy or incite a riot or something and see how things respond to that? Can you sneak into forbidden areas, knowing that there aren't going to be any permanent penalties to getting caught?
The biggest question I have, though, is about the other players. Who are they? What are their characters? What do they like to do? D&D is a team game and involves a team. Whatever you want to accomplish it's better if it's done as a team game.
'As i just want to roll some dice and slay some monsters. Not role play how my guy gets his head caved in for the 10th time.'
There's nothing wrong with trying to slay monsters. Maybe you shouldn't try to fight everything, though. Since you were GMing before, did you ever make situations or threats where there were options for the players other than fighting? Nothing too tough for them where they might need to find allies, or friends, or resources?
It sounds like you had a player in your GM sessions that wasn't getting what they wanted, that is, more complicated problems outside of ones which are just bashing, and wanted to run a very different session than the ones you were running for them. And now you're in the reverse position, inside a game that isn't giving you what you want.
D&D's a team game, and it's always a mutual association between the entire group, both the GM and the players. People want different things out of it, and finding the right balance and satisfying everyone is always challenging.
Your suggestion that guards should auto-win if they're invincible sounds reasonable, unless you're just entering the city and attacking one immediately. "Describing your character's death in detail" might be something your GM is doing to try and discourage that behaviour. I don't think I'd try that myself, but I wouldn't say it's absolutely wrong.
I would recommend asking on the Order of the Stick forums, but I do have one recommendation: Know who the other party members are, and describe them, too. There's always a give and take between "My GM is incredibly railroady and only has interest in making people explore a Magical Realm" and "This is a player who disrupts the game because he can't go five minutes without getting his hit of combat/roleplay/romance, etc." It's a constant conflict and one very common in all games. They've seen it, and the OotS forums has lots of people who give good advice on the problem.
Not knowing (or caring), who the other players are is a very bad look. If you don't pay attention to your fellow party members you might be the one not paying attention to their needs. Particularly since it sounds like you were the GM for these people.