A word between "several" and "many"

The only word that comes to mind between several and many is numerous. But, inserting that into your example sentence feels a little awkward to me. I think you might be better served by simply saying "A cycle time of 10 to 30 seconds is achievable." Especially in light of the fact that pieces of technical writing should, in my opinion, avoid the usage of vague terms like the others in your list.

If you're set on using an adjective, you might consider reworking the sentence to give yourself some other options. For example, "A significant/substantial cycle time is achievable.

a fair few OED:

P.1.e. colloquial

(a) Used as noun: a considerable number; also with of-phrase as complement.

2006 L. Welsh Bullet Trick (2007) 77 Glasgow's got a hostelry on every street corner and a fair few in between.