When the sequence ^[[5~ starts printing I press Del button, the sequence ends with a ^[[3~ and then Zorin boots normally.
If I miss the 1st process then it starts printing "dev/sda5: clean: / files: /". In this case pressing Del only won't work, so I have to press ctrl+alt+del - it takes me to the grub menu and from here when I click enter on Start Zorin it boots normally then.