first bisection step takes quite a while

Hello,

today I did a bisection in the kernel repository:

	linux$ git version
	git version 2.47.1

	linux$ time git bisect start 09fbf3d502050282bf47ab3babe1d4ed54dd1fd8 96d8eab5d0a1a9741a4cae1b3c125d75d1aabedf
	Bisecting: 572238 revisions left to test after this (roughly 19 steps)
	[eafdca4d7010a0e019aaaace3dd71b432a69b54c] Merge tag 'staging-4.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging

	real	18m41.374s
	user	27m18.306s
	sys	1m0.565s

I was surprised that it took that long to find and checkout the first revision to check. (That is on a 4 x Intel(R) Core(TM) i5-6440HQ CPU @ 2.60GHz, 16 GiB RAM with a Samsung SSD. On a different machine (56 x Intel(R) Xeon(R) CPU E5-2660 v4 @ 2.00GHz, 256 GiB RAM and (I think a spinning hard disk)) it took nearly an hour.

I think this isn't my first bisection over that many commits, but I cannot remember that the first step ever took so long.

Is my expectation (and maybe memory) wrong, or is this a regression?

Best regards Uwe