You don't really need to leave it that long. 10-30 min is fine, if you're short on time 5 min is also fine.
Don't over-use the Renovateur, you don't need to apply it every time you polish your shoes. If you're using it on a new pair where you don't know how the leather will react, test it on a small hidden spot first. There have been plenty of mishaps with this product, don't buy into the 'liquid gold' rubbish.
Thanks @te0o
I may leave it for some minutes more than the '3 min' mentioned so.
I have used Saphir Renovateur previously on several pairs. I am happy with it overall. Let's say I use it once per month.
It's just I wanted to know if I could apply a little bit more or more often during some time to soften a little bit the leather. It's tough walking all the day with relatively stiff leather shoes on cobblestone streets.