9 x 10 minutes is not very practical and you don't get very deep usually with 10 minutes.
On the other hand 1,5 hours is a bit long.
2 x 45 min sittings, one in the morning and one in the evening, if it is possible for you, would be perfect.
Of course it is also good to try to be mindful when you are not formally meditating.
(For example in waiting times.)
I can only hold good concentration for about 2 or 3 minutes .
What do you mean with this? If your mind wanders away after 2 minutes that's perfectly normal, no reason that you can't meditate longer. Just bring your attention back, again and again.