I would agree with the previous poster... if you are connecting onto a budget airline who has no agreement with US, 2 to three hours is sensible. However if you are connecting to BA,BD,EI etc who have baggage agreements with US, 90 mins should be fine as they should be able to through-check your bags in the States. Even if you have to change terminals, there are only two; and it's only a 5-minute ride on the monorail from one to the other. Hope this helps!