An Elixir of Travel grants Travel Time when consumed. They are sometimes given out as event prizes and some can be crafted (sometimes spending your own travel time to create).

Sources

One of the possible gifts in the Winter Wonderland Event.

They can be traded to other players.

Milky Elixir is also used in the Blessing of Isis.

Milky Elixir can be created in a Chemistry Laboratory.

Currently, there is no way to create any of the other types of Elixir

Use

Click on Self > Skills > Consume... > Elixir of Travel (type). You will get a main message that says:

You have consumed an Elixir of Travel (Clear) and have gained 12 hours travel time.

You have consumed an Elixir of Travel (Diamond) and have gained 30 days travel time.

Varieties

Type	Travel Time	Source
Milky	1H	Events, Chemistry Laboratory
Clear	12H	Events
Glass	1D	Events
Crystal	7D	Events
Diamond	30D	Events, Alchemy?