Weekday dim sum in Houston
I'm not sure which of the big cart style restaurants are open on weekdays, but you can definitely get dim sum at a few places that cook to order. It's not as exciting as ordering of the carts, but the flip side is that everything you get is fresh out of the kitchen, which is a worthwhile trade off in my book.
I'm not sure where you are coming from, but I would recommend Yum Yum Cha in Rice Village (2435 Times Boulevard) or HK Dim Sum on Bellaire in Chinatown (9889 Bellaire Blvd # 110). I really like both. Yum Yum Cha is a little more expensive, but they have my favorite eggplant shrimp. HK Dim Sum has slightly larger portions and is also excellent. I think there are a few more places like this in Chinatown (maybe one in the plaza across the street from HK Dim Sum), but HK is my favorite.
Yum Yum Cha Cafe
2435 Times Blvd, Houston, TX 77005