What is \$V_{ADJ}^{+}\$ and \$V_{ADJ}^{-}\$ for this adjustable delay schematic?
The upper and lower MOSFETs in conjuntion with their respective 200 kohm resistors act like current sources. The voltages on their respective gates make the current they can provide higher or lower. So when one or the other middle MOSFETs activate, one or the other outer MOSFETs delivers current to charge up (or down) C\$_{ADJ}\$ and the current forms a ramping voltage.

If that current is variable then the ramp can be made quicker or slower thus it takes less or more time for the output MOSFETs to switch.

If you want a fast rate then connect -V\$_{ADJ}\$ to Vdd and +V\$_{ADJ}\$ to ground. If you want a slow rate then connect them both to midrail.