[Closed] Electronic circuit help

I've got a car stereo that you can plug USB memory sticks into. Only problem is, I want to plug a USB HD into it. Now this sort of works after a bit of hacking, but the problem is that if you have it plugged in when you start the car, it often doesn't work.

I've already had to make my own power supply for the HD (using a voltage regulator) but it's not ideal so I'm going to replace it. However, I want a delay of about say, 90 seconds before the power to the HD comes on.

This is what I came up with - can someone tell me if I'm anywhere near, or is it bobbins?

[img] [/img]

EDIT: thinking about it, for that to work the cap would have to be pretty big, since it doesn't take much voltage to open the gate, does it?