The first thing to know is that you require an ESTA clearance to enter the US. This must be done 72 hours (or more) in advance.
http://www.smartraveller.gov.au/zw-c...y_Requirements

As for the time, unless you go real early there is no way you'll get from Vancouver to Everett in 2 hours. 3 is more like it, and it may well be even more as the border crossing is currently subject to a major construction project. Other than in the middle of the night there is no guaranteed way of predicting 'good' times for crossing, it really is hit-and-miss.

There's a website which monitors (live) the traffic:
http://www.borderlineups.com/cam.php?RegionID=1

There are some times (Fri and Sun afternoons, Sat mornings) when delays are very likely, and obviously holiday weekends should be avoided at all costs. The smaller crossings (Linden, Sumas) are usually less crowded, but I wouldn't recommend them for non-US/Canadian passports - the agents there don't see many 'foreigners' and will likely give you a more thorough umm... examination. Quite a way off the direct route anyway.

EDITED TO ADD: I'm told I'm mistaken about ESTA and that for land crossings it is not required. I don't know where this is specifically stated. Best to check for yourself (US consulate).