The main thing here is: once again make certain the surface is clean and free of dirt and oils. Remember, you are basically working with skin, Just like your own skin, if you clean it but do not moisturize it, it will get dry and start to crack. And it would be a bit gross to think about rubbing lotion a dirty arm or leg. It is the same with leather. Do not just clean it without putting on a moisturizer afterward or condition without cleaning.
It is true that most modern leather surfaces have a light plastic (urethane ) coating to help protect the hide; however this is also susceptible to drying and cracking as well- and if it goes South, your interior will look sketchy. Clean and Moisturize every month or so and things will stay looking and feeling great.
If your car is older, it will not have a urethane coating and will be much dryer due to the additional years it has spent battling the elements. Therefore, you should leave the conditioner on the surface for a few minutes, maybe 15 to 20 to allow the ingredients to absorb into the leather’s pores. This will hydrate the hides and get them feeling right again. With newer treated leathers this will not do you much good, as the pores have been sealed with the coating which is moisture and waterproof. None the less, it will help the surface of the coating stay in great shape.
The take away is; if you Don’t have time to both clean and condition, it is probably better to wait until you can do them together.