Worldhopper

A Worldhopper is any character from within the Cosmere books who is capable of 'traveling' from locale to locale in the Physical Realm by the use of some form of Investiture. Likely, this is achieved through access to Shadesmar (i.e., the Cognitive Realm).

Brandon has addressed Worldhopping; essentially, there are three ways Worldhoppers are able to do what they do:

1) Some are functionally immortal. They do not age.

2) Some age very, very slowly.

3) Some benefit from relativistic effects.

Hoid is likely both 1) and 3).

The only time manipulation for which there is solid evidence is in Allomancy, bendalloy and cadmium (within The Alloy of Law, Shadows of Self and The Bands of Mourning), and that's effectively a relativistic effect. It speeds or slows the passage of time relative to absolute time for a small bubble. This could be used to travel forward in time, but cannot be used to go back.

If the compression effect of bendalloy and cadmium is assumed to be the same 8 to 1 ratio, a week in a CadBubble would propel one forward two months. Not a huge leap really, but if one is functionally immortal from Atium burning, breaths, or some other Investiture, it's reasonable.

There may be Surges, Awakenings, glyphs of some other Investiture that allows other effects, but they have yet to be seen.

Hoid
Hoid is a reoccurring character that shows up in every Cosmere series, who is originally from the Shardworld Yolen. His motives remain unknown, although it has been concluded that he is looking for something unknown. Hoid's full origin will be revealed in the Dragonsteel series, although we do know that Hoid is not his name and has gone by many aliases.

He has collected a variety of Invested items from around the cosmere and gained access to multiple Invested Arts. He has written to Frost, Endowment, Autonomy, and Harmony, hoping to enlist their help in dealing with Odium, though only Harmony has responded positively. He has some ability to manipulate Fortune, which lets him learn where and when he needs to be to advance his goals, though he often doesn't know why being somewhere is important.