How long do I have to wait to get new skins?

When you play a game with unknown signals enabled, from time to time the game will generate a vessel or "thing" that emits either a weak signal or a strong signal. The time for this things to spawn are server defined, so this is not the focus here.

However, when you press the button on this spawned thing, it sends a signal on steam, which makes you randomly get skin items (that can even be sold on steam market).

How long do I have to wait to press either the strong signals or the weak signals and kind of guarantee that I will get something?

Strong signals have better skins. On multiplayer games, a different weak Unknown Signal will spawn for each player, and it'll only appear on that player's HUD. It's still possible, though, for other players to find and use the Unknown Signals that do not belong to them. The strong signals are global, visible for everyone.

The chances of a strong signal spawning instead of a weak one are 10% for each player, meaning the more players there are, the greater the chances, as those signals are global and not bound only to the player that caused it to spawn.

Weak signals spawn between 1.5 and 4.5 km from the player, while strong ones spawn between 20 and 90 km.

After an Unknown Signal spawns, a 15 minutes countdown starts, and the Unknown Signal disappears once it's over, if not interacted with by a player.