Use chrono::DateTime for secrets

[A6GibKm]

I am not sure if adding another dependency is desired.

Its somewhat weird to return the number of seconds since the unix epoch in anything but as a date.

[bilelmoussaoui]

I am not a fan of depending on chrono for this very small bit; using Duration is fine and people can convert it to a date using whatever library they are using

[A6GibKm]

Ok then ill add the methods as duration

[A6GibKm]

Done.