No, its fine honestly mate.

what is your purpose of the delayed relay?

in my opinion your using the correct relay.

if the expansion tank isn’t baffled and your doing some hard cornering on track for instance, it may trigger the coolant switch when the water is forced to one side, so the time delay will stop it alerting you of a false alarm and triggering the light and buzzer straight away.

although I’d not have the time delay too long, I’m sure around the 15 seconds mark is more than enough to take into account a very long corner, but short enough that if you had a hose go and let all the coolant out it’d give you a chance before it was too late.

it can always be fine tuned on the relay if you do get any false alarms with that duration.

On another note your set up may not necessarily need a delay, you could make it just a couple of seconds because the float hight is enough that cornering doesn’t cause any issues, and the the tank is small enough that the water level doesn’t shift much.

food for thought anyway 👍