You can’t use a timeline in this case. You need a variable which determines your speed and some logic which makes your character spin all the time by that value. If it’s 0 you can skip applying it but in general you need to hook your logic up to event tick.
Since you’re only changing the pitch you might as well just get the current pitch, add YourVariable to that and set it as your new rotation on event tick.
The higher YourVariable is the faster it will spin. Pressing can then just slightly increase it each tick and you have exactly what you wanted.
Cheers