A word on duty schedules:
Page one of this Q&A thread contains the duty schedule, which shows who is in charge of every department during any given shift. The number one reason this exists is to help provide a quick reference for our players; that way, you will know when your character has command, when your character is expected to be on the bridge, or you'll be able to quickly see who would be at a given station at any given time. This helps us have in-universe consistency across everyone's posts.
Understand though, that the schedule is NEVER meant to limit the game or prevent you from playing.
For instance, I'm about to make a post as Captain Drake for 2/15. According to the schedule, Drake has command on Saturday Alpha - and Ltjg. Reid is the only other PC on duty. Literally every other department head is off shift at that time (most get Saturday off).
Well, we are due to arrive in the Calican system during Saturday Alpha. So does that mean that you can't post?
To the contrary, it's generally understood that on "important" dates that we are aware of ahead of time, all senior personnel are to be on duty. After all, you work for Starfleet - not the local mechanic shop or bakery or whatever. Generally, we will always want to have the most qualified people avialable in known situations of demand. So you can expect to be on duty, figuring that you'll trade shifts or whatever as best you can. Remember that lives can and do depend on your character doing their job, so sometimes, you just may have to work some overtime.
That said, there is some leeway here. Merideth has posted that this is Callie's off day, and she's already talked this over with the aCEO. Truth be told, Lt. Sa'eridon is certainly plenty qualified to oversee repair of a navigational beacon, so Commander Kennedy is perfectly fine maintaining her schedule. On the other hand, we would probably expect to have more senior staff at the helm, at Ops, etc than a handful of NPC enlisteds... at least when we enter a system for the first time. Just in case.
So, bottom line - if it makes sense for your department head character to be on the bridge in am expected, planned situation... you should assume that they are there, no matter what t he schedule says. The schedule is more for dealing with the day to day scenarios.
Make sense?