If you are on Vista or Windows 7, there is a better way to launch MC at startup, and yes, you can have it delay as long as you want. Instead of launching it the way you're doing it, use the Task Scheduler to launch it.
I use the Task Scheduler to launch almost all of my startup items. It is convenient, easy to use, and powerful.
1. Click Start and type task scheduler and hit enter.
2. I like to make a folder for all of my Startup Items. You can do this if you wish. This makes it easy to disable all of your startup items at once if you need to (you can enable/disable whole folders).
3. Create a basic task, using the panel on the right.
4. Follow the wizard, choosing "when I log on" as the event, and putting MC's exe and command line options in the program fields.
5. On the last page, check the "Open Properties panel" checkbox and click Finish.
6. Switch to the Triggers tab, and click the Edit button to modify the "At Log on" trigger.
7. You can add a configurable delay here of 30 seconds to 8 hours.