"kasp" system test is failing consistently on Windows

The same four checks always fail on Windows:

kasp1.log-I:kasp:check next key event for zone step2.algorithm-roll.kasp (570)
kasp1.log-I:kasp:error: bad next key event time 20909 for zone step2.algorithm-roll.kasp (expect 21600)
kasp1.log:I:kasp:failed
--
kasp1.log-I:kasp:check next key event for zone step5.algorithm-roll.kasp (594)
kasp1.log-I:kasp:error: bad next key event time 24513 for zone step5.algorithm-roll.kasp (expect 25200)
kasp1.log:I:kasp:failed
--
kasp1.log-I:kasp:check next key event for zone step2.csk-algorithm-roll.kasp (618)
kasp1.log-I:kasp:error: bad next key event time 20916 for zone step2.csk-algorithm-roll.kasp (expect 21600)
kasp1.log:I:kasp:failed
--
kasp1.log-I:kasp:check next key event for zone step5.csk-algorithm-roll.kasp (642)
kasp1.log-I:kasp:error: bad next key event time 24519 for zone step5.csk-algorithm-roll.kasp (expect 25200)
kasp1.log:I:kasp:failed
--
kasp2.log-I:kasp:check next key event for zone step2.algorithm-roll.kasp (570)
kasp2.log-I:kasp:error: bad next key event time 20956 for zone step2.algorithm-roll.kasp (expect 21600)
kasp2.log:I:kasp:failed
--
kasp2.log-I:kasp:check next key event for zone step5.algorithm-roll.kasp (594)
kasp2.log-I:kasp:error: bad next key event time 24559 for zone step5.algorithm-roll.kasp (expect 25200)
kasp2.log:I:kasp:failed
--
kasp2.log-I:kasp:check next key event for zone step2.csk-algorithm-roll.kasp (618)
kasp2.log-I:kasp:error: bad next key event time 20962 for zone step2.csk-algorithm-roll.kasp (expect 21600)
kasp2.log:I:kasp:failed
--
kasp2.log-I:kasp:check next key event for zone step5.csk-algorithm-roll.kasp (642)
kasp2.log-I:kasp:error: bad next key event time 24564 for zone step5.csk-algorithm-roll.kasp (expect 25200)
kasp2.log:I:kasp:failed
--
kasp3.log-I:kasp:check next key event for zone step2.algorithm-roll.kasp (570)
kasp3.log-I:kasp:error: bad next key event time 20936 for zone step2.algorithm-roll.kasp (expect 21600)
kasp3.log:I:kasp:failed
--
kasp3.log-I:kasp:check next key event for zone step5.algorithm-roll.kasp (594)
kasp3.log-I:kasp:error: bad next key event time 24539 for zone step5.algorithm-roll.kasp (expect 25200)
kasp3.log:I:kasp:failed
--
kasp3.log-I:kasp:check next key event for zone step2.csk-algorithm-roll.kasp (618)
kasp3.log-I:kasp:error: bad next key event time 20943 for zone step2.csk-algorithm-roll.kasp (expect 21600)
kasp3.log:I:kasp:failed
--
kasp3.log-I:kasp:check next key event for zone step5.csk-algorithm-roll.kasp (642)
kasp3.log-I:kasp:error: bad next key event time 24545 for zone step5.csk-algorithm-roll.kasp (expect 25200)
kasp3.log:I:kasp:failed

I am not sure how long this has been going on because another Windows-specific issue (!3184 (merged)) has been masking this problem.

@matthijs: I have not yet looked at this problem closely, please take a look if you have some time. Keep in mind that the kasp test takes a lot more to run on Windows than on Unix systems (about 15 minutes; yes, you read that right). We will need to get this fixed before tagging or else we will have trouble producing release tarballs (as CI pipelines will not be able to pass).