Unless are using a truly slow lens or a very archaic DSLR it is quite unlikely that will need to take 5' or longer subs.
Anyway, the practical limit for exposure with these devices is given basically by three parameters.
First and foremost, the sky/target brightness (you do not have to take the longest subs, but the rightly exposed subs. I could, but do not take 5' subs because this would mean "burning" the brighter areas).
Second, the accuracy of your alignment to the pole
Third, the tracking device intrinsic mechanical accuracy.
If are good with the polarscope, and take your time to trim it, you can attain a polar alignment good enough for 5' at 200mm; however it is highly unlikely that the mechanical accuracy of the Star Adventurer will allow you to take such subs without trailing.