The temporal rift is an optional zone accessed via a portal on the third level of The Daikara. Once you enter the rift, you cannot immediately return to Daikara or the World Map via an exit or the Rod of Recall. In addition, if you die in the rift on Adventure mode with lives left, the Eidolon will not give you the option to return to the World Map. Therefore, be sure you are fully prepared before entering.
The temporal rift is split into several zones. The first is a zero gravity zone filled with telugoraths (time elementals). The difficulty with this level is that movement is 3 times as slow, so try not to move when an enemy sees you, otherwise they will get in 3 free attacks. Telugoraths are magic users and will cast spells. The telugoraths can try to "swap places" with you, and leave you confused. The enemy themselves aren't difficult if you fight them 1 on 1. Fortunately, your vision extends extremely far and is not inhibited by the walls here, so you know where all the enemies are around you.
For melee users, you need a way to quickly close the distance (move runes, rush), or at least stay behind a corner and wait for them to come to you. For magic users or archers, just stand still and shoot at what you can. As long as you remember not to move, then you should be able to beat it fairly easily.
The fourth level is the Lake of Nur (1st level, where you are above the lake and not underwater). Here you will fight the Chronolith Twin and Chronolith Clone (chronomancy magic users), which are the final bosses of the zone. After defeating them, you will receive The Rune of the Rift. In addition, you will unlock the Temporal Warden class, if you haven't already done so.