Here is a guide to What They Really Mean What They Say (Part 1):
When they say: Get it done whenever you get a chance.
They could mean: I really need it within the hour.
But they could also mean: I’m giving you nonsense busy-work since I can’t think of anything else for you to do.
But they really should have said: I’d like you to finish this task within the hour because I’d like to proofread it before I email it to my boss later today
And they didn’t say that because: They worry that you will think they’re too demanding and pushy if they are too direct.