1. Precise change over time: Use the timer behavior and lerp.
On collision - start timer for 5 seconds
Timer is running - Set value to lerp(0,100,Self.Timer.CurrentTime/Self.Timer.Duration)
On Timer - Set value to 100
2. a. You can use the "Wait" action to delay following actions
On collision - Set Variable to 8, Wait 3, Set variable to 10
b. Or you can use a timer behavior once again, and On Timer set value to 10
On collision - Set Variable to 8, Start timer for 3 seconds
On Timer - Set Variable to 10