I use an electronically controlled flasher can,
which is controlled by a microcontroller which
is temperature compensated so has an exact delay.
It also incorporates 2 adjustable knobs on the dash
i can use to further 'tune' the indicator time.
One says the on time, the other the off time.
So when i'm feeling kind of daring, i'll turn the
speed right up, but for sunday cruises i like to have
it real slow.. (around 1--2 seconds off, and a big lazy
4 second on)
I can also simulate 80's white vans changing lanes
with a .1 second on time and a .8 second delay.
These flasher cans come complete for $49.95 with mounting
bracket and 1.2 m of connecting wire. (available in red/blue anodised aluminium, or powder coated black.