Hey, Charabby...sounds like a great trip! I live in Pasadena, and though we don't go to DL often, we go past it on the way to Legoland
Under the best of circumstances, Pasadena to the DL offramps from the freeway would be about 45-50 minutes. In bad traffic, you can about double that; virtually any of the freeways there has the potential to get really nasty. The key is careful planning; for example, during the Rose Bowl game is a fabulous time to drive (barring accidents)! The route Judy mentions is one possibility, and probably the one many mapping programs will give you, but there are better ones, especially if you have a family in the car and can take carpool lanes. Our personal favorite is going down Rosemead Blvd. to the 60, then east on the 60 to the 57. The 57 has a good carpool lane from there, tends in any case to be less crowded than the 5 or the 605, and has fewer trucks than either of those. The 60 can have some bottlenecks and does have lots of trucks, but patience gets you through, and it is better than the 10 as a general rule. The 210, which runs through the middle of Pasadena, is good, but it takes you rather too far to the east before it connects to the 57 (better connection with the 605, but I do loathe that freeway!). Anyway, that's lots more than you wanted to know, but it is to give you an idea of options; as long as you are comfortable with freeway driving, you'll find it to be a very reasonable trip.