Ukemi (falling practice) is not some onerous aside that we have to get through at the beginning of class before we can go on to the real judo.
Ukemi is actually closer to being the main event - the most valuable physical skill and the most beneficial practice form that we do. It is far more important to get good at mediating impact than learning 20-30 ways to knock someone down or choke or bend an arm.
Accordingly, the ukemi practice at the beginning of class needs to be slow and careful and deliberate and thoughtful. Avoid jumping into the ukemi to get it over with. Instead, pay attention and go slow enough that you can get very intimate with every aspect of each falling form.
Whenever you think that you've got a handle on ukemi and it is becoming boring and commonplace, cut your rolling speed in half and all of a sudden a whole new crop of issues will pop up. In this way you can keep your ukemi practice challenging and productive forever!