Relay Switching on Delay

Just buy an on-delay relay. Plenty available.

You could buy an auxiliary base for octal relays, delay on or off. Quite cheap from what I remember.

why reinvent the wheel?

If the coil is DC, by adding capacitor parallel to relay and protecting it with discharge resistance across it you can achieve the delay. Either calculate the time constant of RC circuit to calculate value of C or try with hit and trial, starting with say 100µf and increasing by adding more in parallel to achieve desired ON Delay.

There will be Off delay also. This can not be made instantaneous but reduced by reducing value of discharge resistance.

Above is very crude method and not suggested for any electrical safety or repeated switching.

In case of relay in any safety or protection system, we get readily available timer add on for DC Control supply .

Both On delay and Off delay are available (for example from Omron and not expansive).

Also adopting the timer in existing panel is very simple. The timer has just two terminals and is connected in series with the existing relay to which we have to add the time delay. (Just open the positive to relay, connect it to +ve of Timer, and connect a wire from negative of timer to +ve terminal of relay. So just adding one wire - so simple and your existing relay becomes time delay relay)

Thank you !

Forget to mention the coil is 230 V AC.

Usual timers are not cheap for my aim, but I will search for those "octal" bases !

They are available off-the-shelf, next day delivery from a number of electronics distributors (names withheld). A simple internet search is all that is required. Several of these distributors have so many available that they will sell them just to get rid of them....