Hmm... I'm cheating of course but;
My boot times are <2min. for sure, but then Nickel has no real interest in my external uSD card, or the over 6000 ebooks in 28 folders, that it contains. They are for Koreader's use. Besides, Nickel can't even read some of the ebook formats and would find fault with some that it could otherwise read (so much so that it can't process the SD card with any of those files).
I leave my external uSD card in and switch between Nickel (Kobo's user interface with its two reading programs, database, ect...) and Giorgio130's port of Koreader, all the time. The return to Nickel is a reboot. So, I am probably doing more booting than most.
At present there are a number of tricks, tweaks, and hacks involved to have every thing working smoothly, as mine is now. I intend making a "How To" thread or an addition to the Koreader thread in the Developer's sub forum.
https://www.mobileread.com/forums/sho...d.php?t=216960
The modding to isolate the external uSD card from Nickel and allow Koreader to read hidden files/folders, starts at page 16 of the thread.
Luck;
Ken