Does the minister need to lock up?

I'm currently at church. Alone.
I was also at church until midnight last night.
But I'm not trying out for youth minister of the decade, have boundary issues nor trying to avoid a teething baby...

Instead, I'm doing an essay.
A you're-due-at-midnight-so-I'll-finish-you-tonight-even-if-it-kills-me essay (thus the lack of posts lately!).

Lately I was wondering about ministers and the "duty" of sticking around. Do employees of the church need to be the last to leave the building every Sunday night... or...
If someone else is fine to lock up, then can they leave promptly after the service?

I've found that I'm usually, by coincidence more than anything, the last one to leave. In fact, it's the history of those I've known in ministry.

And I don't mind.

BUT, should it be a requirement?

A while ago I wrote what the roles of a minister should be and what you get when you hire someone... So... 
If, being in paid ministry comes with added responsibilities, should the answer be yes?
If, being in paid ministry means that you're meant to be available for someone (without camping out at the church 24/7!), should the answer be yes?
If, being in paid ministry means setting an example of I'll-help-pack-up-servanthood, should the answer be yes?

If the answer is no, a minister can leave "early," is that the expectation within most churches?

I'm not sure either way...