To get 30 seconds, you need to change the timing resistor (pins 6 & 7 to +V) to about 300k. To make the circuit do what you want, connect the cathode of a 1N4148 diode to pin 2. Connect a 100 ohm resistor from the anode of this diode to pins 6 and 7. This will prevent the 100uF capacitor from starting to charge until you release the pushbutton. It worked on the Spice simulation I ran. The 100 ohm resistor is necessary to limit the discharge current through the diode if you happen to push the button again while the 100uF cap is charging.