reftype 3 means Time
The slot refreshes on a fixed timer, whether or not the user is active.
When to send it
Use 3 for a slot that loads a new ad after a set interval, regardless of activity. Always pair it with RefSettings.minint, the minimum number of seconds each creative stays on screen, and keep Refresh.count accurate so the buyer can see how deep into the session the impression is.
Timed refresh is where buyers are most sensitive, because a tab left open in the background can generate impressions nobody sees. Many buyers discount it, cap it or require a minimum interval. The value is confused with 2 (Event) when a page polls for content on a timer and reloads the ad with it. That is time-based refresh and should be declared as 3.
Example
{
"imp": [
{
"refresh": {
"refsettings": {
"reftype": 3
}
}
}
]
}Fields that carry it
Other values in auto refresh triggers
The auto refresh triggers list page explains the whole list and its common mistakes.