Clock tower activated.
Now i'm in the garden tower present but at a specific location the prince says "I'll must be back on an other age" (approximative translation I'm using the french version).
Do I have to go back all the path to a portal (I have some difficulty to find a way back) and come back in the past or do I have a shortcut to a portal that I could have missed to a portal ?
I'm exactly sure where you are but I have an idea.
You don't have to go back the way you came. I did that my first time and it was a waste of time. You're going to want to work your way to the rock you see in the middle of the area you are in. To get there, wall run as far as you can go on the wall to your right. Once in this area, you should see a pole (or tree?) close to where you are. Make sure you line up the prince with that pole and then jump to it. From there, I believe you jump to your right to land on a bar. Once on the bar, line yourself up with the plank sticking out of the rock and swing jump to the plank. You'll figure it out from there. Oh, get ready to die a few times...the dahaka will be after you shortly
I hope this was the area you are speaking of.