Valentines Day during the day will be slow I think. But I'm thinking after people get out of work it will be busier than normal for a weeknight. Not noticeable but not empty either. Just an guess but who knows til it happens.
With the 2fers going on right now its a good idea to avoid the parks on the weekends. Yesterday it was packed in both parks. TOT had a 75 minute wait and Monsters had a 65 minute wait at one point too! And DL was packed -- in fact we got diverted back stage behind Main Street in order to exit the park! Normally the park thins out by Sunday evening. This didn't happen last night perhaps because some schools have today off for Lincoln's birthday.
I've found with Nemo the line correlates to how busy the park is. If the park is not busy the line is no more than 30 - 60 mins. If the park is packed then expect to wait at least 1 - 2 hrs at least. There is no fast pass.