Arknights is a tower defense game, correct. And not the casual kind, too much tactic. And right now is, pretty much, the best time to join in on the fun since it's an anniversary)
To do the dailies you would need to invest about 5+ minutes of "active" gameplay (setting things up on base, choosing the stage, buying in store, stuff like that) and about 10+ minutes of idling while the game wastes energy on the stage you set up
If you start now - Highly recommend you to waste it on event stage since it give event currency depending on the energy you spent, higher stages only have a chance to drop higher tier stuff, and that's the only difference.
It's safe to say that arknights take less than 30 minutes a day, but it will be higher while you are new since you will, pretty much, regenerate energy as fast as you spend it because of lvl ups.
No teams or guilds. There are friends system that allows you to add their unit to your team and exchange clues for trade points (negligible).