WHAT IF you're scheduled to work on Sunday? And the question this implies: Is the old Sabbath still in effect today for Christians?
this to find a good reason). But you are indeed to reserve and guard the time for the gathering of the assembly, which, in God's wisdom and since God raised Jesus from the dead on the first day of the week, happens to be Sunday (and it's no small fact that the church eventually confirmed this day too). The day itself isn't sacred. The time and space set aside for the gathering of the elect is.
This is why Christ's disciples "need corporate worship to keep them strong" (as commonly expressed). God decided it would be through these means so to do. If a Christian is asked to work on Sunday, she does so. But she may want to make it clear that she'd prefer not to work during the time the church gathers (the principle still applies even if her Christ-community gathered at some other time during the week). We work when we're scheduled to work (with all due respect to Eric Liddell [but, damn, that's inspiring]). And you let your bosses know that you'd prefer not to work Sunday mornings, since that's when your community gathers (I assume for the sake argument). Going in right after the services let out is of course a perfectly viable option.
As an aside, the ancients (Israel included) reckoned the close of the day at sundown, not at 11:59 p.m. So, technically, if you are sabbatarian, you couldn't work from sundown Saturday to sundown Sunday.
Being scheduled to work on the Lord's Day is not a test from God to prove your sabbatarian mettle. But it could be a test from him to prove your standing up for what he has commanded you to do—not forsaking the assembly. And this "not forsaking" isn't a checklist thing, that is, going to church every Sunday. It's a way-of-life thing. To forsake the assembly is to consistently forgo—when you are able—gathering with God's elect for the purpose of re-coventanting together in the name of our triune Lord.