Hi Creblue, I was told that they need to stay on for 6 weeks (or whatever length of time your OS says), but that if you are active during the day then they can be taken off for short periods of time. You are supposed to wear them when you are sleeping as your blood becomes more sluggish, therefore you are more at risk of clots etc then. This is only what I was told, but I am sure that there is far more info around.
I was also told that they must never be rolled down, nor must there be any wrinkles round the calf region as this can cause a problem too.
I take mine off when I go for hydro (obvious reasons), and keep them off until I go for a lay down in the afternoon. Also I am going to go get my hair done next Wednesday and refuse to sit in the hairdressers with them on so I will leave them at home then.
Your choice really, but it is sooo nice to take them off for a while each day.