DC motor - Controlled over-current - how much??

I have a 1 hp 180V DC spindle motor rated at 4.5 amps.
In the drive manual they show over-driving the motor for up to 160%
rated current, but they don't say for how long.
The drive will over-current for up to 300% (14amps)
Higher current is only needed for brief (less than 2 minutes) and
only when drilling with large diameter drills which is rare.

How much can I go over the rated 4.5 amps and for how long?
There is a "Temp rise" rating on the motor plate of 25C.
What does this mean and can I use it to estimate my overload capacity?

Thanks
Joe V.