you can build a oneshot which should be pretty stable over temp, or you can draw a few slow inverters (normal nmos, pmos = 0.25/25).
the slow inverters are fine if the voltage and temp in your system are reasonably well controlled (20% voltage, 50-80C temp range). if these parameters vary a lot, you may want to use a oneshot which can be built so the charging current is proportional to mosfet threshold and independent of vcc.
for example, you can use a nmos vth - reference to make a current to charge a small cap (1-2pf, made with a large pmos gate). the threshold would be another nmos whose gate is connected to the cap. now the vth reference keeps the current independent of Vcc, and the change in vth with temp changes the current to be proportional to the change in the nmos threshold, giving pretty constant oneshot time over temp.
now you only have to worry about the cap varying over process.