The rules for Blink specify that you come back to the material world at the end of each turn and when the spell ends. So what happens if the spell is used out of combat, since there are no turns? Do you only pop back after its 1 minute timer expires?
You pop back about every 6 seconds
At the start of your next turn, and when the spell ends if you are on the Ethereal Plane, you return to an unoccupied space of your choice that you can see within 10 feet of the space you vanished from.
Many spells are written with combat-use as their assumption. However, that doesn't mean we can or should just ignore the parts of spells that refer to things like "rounds" and "turns" when out of combat. Instead, it is fairly simple in this case to translate that "turn" into non-combat terms.
A round represents about 6 seconds in the game world.
In combat, the time from your turn to your next turn is a round and is about 6 seconds long. This means, then, that the character would be blinking back into the material plane at most once every 6 seconds in in-game time. This would apply to non-combat situations as well.
Thus, the spell modified for out of combat terminology would read:
About every 6 seconds, and when the spell ends if you are on the Ethereal Plane, you return to an unoccupied space of your choice that you can see within 10 feet of the space you vanished from.
Now, judging what counts as 6 seconds in in-game time will have to be a DM call since there is no real guidance on that.
For what it is worth, Jeremy Crawford also agrees:
If it's ever necessary to think of turns outside combat, they effectively occur every 6 seconds or so. For more about time in D&D, see "Time" (PH, 181).