Before you can travel though time, you must first pass Nex's test. Nex is the Gatekeeper of Time, and he lives inside the Old Tree of Tera in Tera Forest. You must defeat him before you can time travel.

When you defeat Nex, the Time Gate that lets you teleport to year 2021 will open.

You will not be granted authorization to travel through time unless you defeat Nex the Gatekeeper of Time.

Ah, you've passed Nex's first test. This means you have earned the right to travel to year 2021 using the Time Gate. You're doing great! What a relief!

Take the Time Traveler's Pocket Watch and go through the Time Gate.

Come back after you've passed Nex's test. Nex the Gatekeeper of Time lives inside the Old Tree of Tera.