I think my first playthrough was at just under 40h. I beat 99% of the side missions, but didn't unlock any ally achievements.

Second playthrough was 99% complete for missions, with 2 ally achievements, and I did it well under 30h.

And mind you, the 2nd playthrough was with a totally new character (soldier class).

I wasn't going to use new game+ but the Spectre weapons made the game much easier so I preferred to keep them. I unlocked 2 Ally achievements on each playthrough.  Kaiden and Tali on normal, Ashley and Liara on hardcore and Garrus and Wrex on insanity. Garrus and Wrex make insanity a lot easier. IMO the two weakest character in the game are Tali and Liara so you want to avoid using them on insanity.

I've reported all the posters who made negative comments about Tali. Expect permabans shortly, gentlemen.

Oh, I like the character. She's my favorite after Wrex. It's just that if you use her on insanity, expect her to die a lot.

i played the game on pc and did not like it

How long do you have to play with a squad member to get the acheivement with them?

You need to do at least 75% of the side missions with them, plus Feros, Noveria and Virmire. For allies other than Kaiden and Ashley, do not do any Citadel side missions until you have the characters you want to get the achievements for in your squad. Liara is the toughest Ally achievement to unlock because you have to leave the Citadel to get her.

dark knight cant wait

Hang on, so do you have to the side missions, or it 75% of the ones you do?