Some hard disks have a jumper for controlling spin up. You might look at how the hard disk is configured.
More exotically, depending on what the 7300 was used for, you can reprogram the PRAM through OpenFirmware to wait a certain interval until the disk is available. However, this should happen by default; it would only have been altered to run a non-MacOS operating system. For example, my NetBSD 7300 required such a patch.
More exotically, depending on what the 7300 was used for, you can reprogram the PRAM through OpenFirmware to wait a certain interval until the disk is available. However, this should happen by default; it would only have been altered to run a non-MacOS operating system. For example, my NetBSD 7300 required such a patch.