Increasing time on the rowing machine

Hey everyone!

I've been using the rowing machine as part of my work out for a couple of weeks now. Doing about 2km in 10mins, average 32strokes/min, resistance set to 4. Reading up on it because I like the machine and I feel like it's giving me a good all body work out - more so than the elliptical.

Because I'm enjoying it so much, I'm looking for a way to increase the time on it - like an equivalent for the C25K that is used for running - a way to get my body used to rowing for 20, 30mins at a time without injuring myself.

Does anyone know if one of these exists somewhere? Or if not, should I work on gradually increasing the time I spend on the machine, and maybe drop the strokes/min a bit lower whilst I do so?

Thanks x