Timing for 600 sec (10min) requires that the product of the timing resistor and timing capacitor values be about 480. If you use a 20megΩ resistor, the capacitor has to be about 25uF. As the capacitor charges toward the 555's upper trip point of 2/3 Vcc (8V) the timing resistor has only 4V across it, so it can only source 200nA. The 200nA has to exceed the input bias current of two inputs to the 555, the leakage of the timing capacitor, and there has to be some current left over to charge the timing capacitor.
That is why you have to use the CMOS version of the 555. Trying to get a 10min delay out of a Cmos 555 is a very marginal design, which might stop working at elevated temperatures....