You should do it when it gets hot quickly or at regular intervals
I clean the fan from the PC once a month.
And from the laptop
Will not be much different, fan is fan
With the Pc you only have to turn a pair of screws and the laptop you have to screw the whole thing.
Periodically.
At what intervals
I do it every 2 or 3 weeks.
Depending on the environment. 1/2 - 1 year