I have installed Kali Linux on a laptop that is running Windows.
That means I now have a dual-boot setup with Grub2 using BIOS with MBR.

In addition I encrypted this linux partitoin with LUKS1.
As a result I have a simple disk layout with 4 partitions:
Device Boot Start End Sectors Size Id Type
/dev/sda1 * 2048 2459647 2457600 1,2G 7 HPFS/NTFS/exFAT
/dev/sda2 2459648 369705747 367246100 175,1G 7 HPFS/NTFS/exFAT
/dev/sda3 369707008 371097599 1390592 679M 27 Hidden NTFS WinRE
/dev/sda4 371097600 488396799 117299200 55,9G 83 Linux

When I turn on this laptop, I can see this on screen:

GRUB loading...
Welcome to GRUB!

And I line that requests to enter a password for the encypted partiton.

After hitting ENTER key I get the Grub menu and can boot either Windows or Linux OS.
Technically the boot process works, however the wait time after hitting ENTER until Grub menu is displayed is ~90sec.
I didn't expect that decrypting partition /dev/sda4 would take ~90sec.
What is the explanation for this long waittime?