Bit gutted it isn't stated tbh, it's quite confusing.
Everyone says it's been a while and it's hinted in the conversation with Orgus that you've been doing alot of wrong things in that time. Which to me would indicate at least a couple of months.
On the other hand, you walk out of the door and your companions are still there. If I was an all evil Sith Emperor, they'd have been out of the airlock almost immediately after, with maybe a couple held back for torturey goodness. But they're in the same place, with your ship just round the corner, indicating you'd been gone a couple of days at most, which would hardly have been missed...
...think I'm overthinking this again.