From time to time
Definition 1 of 1
Pro Tip 1/3Time Span
Refers to things happening periodically over the long term, not just once. 
She takes a solo trip from time to time to reconnect with herself.
Pro Tip 2/3Not Predictable
Events occur without a set schedule or pattern, making them unpredictable. 
Meteor showers appear from time to time, without exact regularity.
Pro Tip 3/3Variation
Used to express that there could be changes or differences in something occasionally. 
His opinions on the matter shift from time to time.