No time penality for layered skills.
Eg. (made-up skills) Heart Making I takes 9 hrs and Heart Making II takes 9 days. But, as soon as you start Heart Making I, Heart Making II goes up by a day. What's up with that? There is NO WAY you can learn the second without the first!
But, if it's necessary, okay. Have a nice day. :)
Okay, even IF it's NOT necessary, it's still okay. :)