We need a lot more information:
motor voltage
motor current
power source for the circuit
What starts the motor? Switch? temperature sensor? etc?
If it is a switch, are you holding the switch down for the entire few seconds? Or do you want to push a button briefly and have the motor run for a few seconds after the switch is released?
If you hold down the button for more than a few seconds, do you want the motor to stop after a few seconds anyway, or run for as long as the button is pressed?
Depending on the answers, this might be nothing more than 1 transistor plus some Rs and Cs.