Since you found it necessary to give my LS member an English lesson let me give you a math lesson...
Chainspell - 300 second recast (5 min) - This is what YG says, I thought it was shorter but I'm not a mage...
Rebirth - who cares recast its too long (you probably cant think outside the box, but look it up if you must know)
60 min in dungeon
60/5 = 12
He did lie, you can actually cast it 12 times if your fast enough, I am sure Guks using some common knowledge realizes you cant possibly die and rebirth within the first second of being in the dungeon. Accounting for cutscenes, wait times for lights you can call it a safe 10. If you cant figure it out from here....
You, fail.
Your inability to wrap your head around this basic concept probably explains your inability to complete the dungeon.