> I didn't count the solenoid as an inductor, and simply pretended
> it was an RC circuit, calculated T, multiplied it by 5 and said that's
> how long it could supply the current. I suppose having the L in there
> would change things. Wouldn't the activation period need to be
> about 1/4 (maybe a bit more) the period of the LC oscillation?

Easiest way to get what you want practically is to try a few caps
of various sizes. For a clock movement, all that's needed is for the
solenoid to activate a ratchet and pawl. Too short a time and it
won't grab properly, too long is a waste of time/energy. 0.25s is
"Mummy Bear". If the 0.2s you're looking needs to be accurate
(how accurate ?), you could use calculations, meaning you'd have
to know all the factors (including eg friction), and I'm sure it would
be quicker to experiment on the bench

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