I don't know how fast you want to ride, but 20/25 days seems very optimistic to me for that distance. Consider, that you might loose on every border at least half a day. O.k., sometimes it can be very quick, but you shouldn't count on that. E.g. the border in the east of Kyrgystan (closest to Almaty) was closed for tourists last year, so you probably need to pass the border via Bishkek. If you want to have a nice and relaxed trip, I would recommend only fewer countries (Kyrgyztan, Tajikistan, Usbekistan), which is feasible in that time at my opinion.
If you have any question, just drop me a message.
Best wishes, Matthias