I'm not ready for 20 min in a row yet either!! I've now done 20 min with several break, and I'm gradually adding tiny intervals to get to 25 min with breaks. Then might start reducing them.
If you have any injuries, then it's worth being careful and not pushing on too much - even 30sec extra can set me back awhile, it seems, if I'm not ready for it. Plantar fasciitis, tendon problems, shin pain etc. come back very very quickly.
When I get to the point of two lots of 10 min, then I'm going start moving the break by one minute each time I think, so that I can tell myself it's the same amount as before, but 11 and 9, etc., until it's closer and closer to 20 all in a row.
I'm feeling a bit fitter now, and heart rate and breathing back to normal much faster, but what doesn't go away is the sweaty red face, for over an hour afterwards. Makes it very difficult to arrange to run when I have various clients in the day, since I don't just have to be back in time, but also for an extra hour or more to let my face approach normal colour and temp. No chance of putting make up on for quite a while, either. I tried the Magic Cool spray, but it didn't help. Don't know what else I can do! It's also really getting to steamy glasses weather, which is embarrasing and makes me look like i'm sweating so hard, when it's mostly just the waether. Can't see very well that way either!