If you've dirty flashed (not recommended), boot time depends on your installed apps and probably the rom you choose. Otherwise, it just takes a few minutes. I didn't have my stopwatch out when i did mine.
I did not do a comparative test on boot times between 4.2, 4.3 and 4.4 but to me 4.4 seems the quickest to boot and I would estimate my b70 tab with no keyboard boots in under 5 min. This has not changed much from first boot.
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