Creating a Sequenced Array of 3 Mosfets with Adjustable Timings
As Anindo says, a small microcontroller (such as a PIC10F, 12F, 16F) is the perfect solution for this kind of task, so if you are up to trying this examples can be given. If you want to progress with modern electronics microcontrollers are pretty much a necessity.  

To do it without one, there are a few ways you could approach this - for example you could set up a logic gate based circuit with a clock/counters/comparators, or you could use a 555/556 based approach. If you don't mind the timing being equal for each FET then a 3-bit ring counter could also be used - the timing for all could be adjusted still by changing the clock speed.

If you know 555s, then you could set up 3 555s in one-shot mode, then use NAND gates to trigger each one in turn. I think this should work okay.
For example, when B and C are low, A is triggered, when C and A are low, B is triggered, and when A and B are low, C is triggered. To adjust timing on each, use a potentiometer for the R part of the RC timing components on each 555.
If you need a diagram, let me know and I'll try and throw one together.