Thanks.
With each tiny step forward I seem to be slowly being backed into a corner of having to learn how to use a PIC.
I doubt, given what I do I'd ever need more than an accuracy of - let's say - 95% (ideally and over optimistically 98%) to put a number on it. Timing accuracy will depend on each circuit in question, I'm just trying to understand SMD options (because I was disappointed to see so few PET/MKT types available at 10uF), so your answer is very enlightening - SMD film capacitors appear to be few and far between, and 10uF was (comparatively speaking) very expensive - hard to justify that for a little hobby circuit, even for decent timing accuracy.
One part of the circuit I'm about to start in a few days only needs to have about 10 seconds on time, but precision isn't important for that; not sure if the other part with the dual slope ADC needs a precise timing capacitor though, even if it's only a 7136, but as that's in the pF range shouldn't be a problem to find.
I've tried to keep timing capacitors to about 10uF and use higher value resistors due to something I read regarding leakage, maybe that doesn't apply so much to PET/polyester film anyway.
Electrolytic are pretty dreadful - like a bad watch spring (I'm so sad: I actually timed on-circuit a 555 astable pulse using different types of capacitor to see if there were any differences...polyester/metal film won by a long shot on accurate repeatability), not sure if the newer SMD ones are as "better than the through-hole version" as I have read they are. And I read that ceramic is not a good choice for timing in general as they have temperature variations and the piezoelectric effect (I think that's the name) causes unwanted oscillations that alter timing.
If for the time being I won't be using PICs or similar, are SMD ceramic and aluminium electrolytic really so improved upon their through-hole version counterparts?
And would you recommend the Tantalum SMD capacitors over the previous two types? - Tantalum gets quite varied reviews in dielectric comparison charts and articles on the subject of capacitor selection by function.
Your answer explains to a degree (besides size and some dielectrics being "young" technologies) the low capacitance range over many of the more appealing dielectric types I've never tried such as PEN film or Niobium.
Once again, thanks.