Generally you have to link him to the two fastest characters on the enemy team. The more turns they take, the more ultimate he builds up. If you connect to the tank and another character taking very few turns, he's not going to hit ultimate.
For example, against LV and his clones, if you link Scorch and LV, he'll get to ult pretty quickly because they take a lot of turns, LV is fast and Scorch does a lot of moves, even as a tank. It would go even faster with Appo and LV.
If you face a Mace team and link Temple Guard and Jocasta, it's going to take longer to build ultimate than against LV teams because Temple Guard is far slower and doesn't move as often. (He doesn't need ult against them, I know, it's just an example)
If you don't link anyone, he's not really going to gain ultimate charge, so if there's one character left, it's gonna be a while, if at all.