Morning application is on for 3-4 hours. Evening application is on all night.
You should keep it on for 4 hours for maximum absorption, but I'm sure if you keep it on for at least 2-3 hours you will be ok----it's probably mostly absorbed by then.
I don't wash my hair every day, so on some days, the morning application stays on all day. I'm never up early enough to apply it and then wash my hair later, so on the days I wash my hair, I just apply the liquid shortly after showering.