Is the following possible?

If the time of day is within a certain range, then boot to CD. Otherwise, boot to HD. Do this *without* any user intervention (e.g. user removing the CD or going into BIOS).

Assumptions:
BIOS can be set to adjust boot order.
customized Knoppix CD is always in the CD-ROM (never ejects).
a floppy drive exists.

Restrictions:
Can't modify the HD in any way.

As far as I can see the options are 1) modifying isolinux on the Knoppix CD -- but how? 2) putting a bootloader on floppy and booting initially from that -- but if I put lilo or grub on a floppy they can't see the CDROM.

I have been puzzling over this for a while and would be very grateful for any ideas!