I don't think tying tech team skill to a time based experience system is such a good idea, as tech team progression would be very linear at the best of times. I think that a better idea would be to link tech team progression to the number of divisions built (for infantry, tank, naval etc. tech teams) and to the actual fighting that you do (for doctrine tech teams). This would allow a more variable increase in tech team skill.
This would mean that Albania, fighting and conquering Greece would gain tech team skill faster than they would under a linear system, which would make the game much more dynamic.
The drawback is of course that it is difficult to measure this, especially for industrial tech teams. You could base them on the amount of industry that you have, or the amount of industry that you build, but this could again be difficult to handle, or simply odd, especially for computer and encryption / decryption tech teams.