Keeping in mind stable regulations and guestimating that a team would improve 1,5 sec year-to-year for a given venue .. 1,5 sec / 52 weeks gives us a weekly rate, times 8 weeks would be around 0,23 seconds/lap. But you can honestly insert whatever value instead of those 1,5 sec. Personally I think over 2 tenths is a bit optimistic.
What can make a bigger difference is if those 8 weeks enable Honda to finilize another spec engine. Then of course the performance improvement can be a step-change. Lets hope that's the case