What's the point of doing a 90 and 90? Why not just do meetings when one can?
I agree with what John said, it's just a suggestion, and sometimes for the alcoholic who needs something to do and somewhere to be, each evening when they might normally be drinking, it can be useful. I understand it's something preached by rehabs, which many in AA have adopted.
Some think if we just say go when you can, then silly excuses like my favorite show is on TV at that time might come into play. On the other hand I have seen some fanatics about this, even here I remember people giving what seemed to be very good and valid reasons, why they couldn't make a meeting every day, and one or two members insisting that's not good enough, you must go. We should be able to judge whether the person really want's sobriety, and then just say do 90 in 90 if you possibly can.
"Good morning, this is your Higher Power speaking. I will not be needing your help today."