A contact lens should not be left in for a period longer than 18 hours at most. This assumes that you have been acclimated to wearing lenses and haven't just begun in the past few days.
The reason that you must limit use to no more than 18 hours is because the surface of your cornea needs to have oxygen and saline. Your tears produce normal saline but they do not penetrate the surface of the lens.
Previous contact lenses were made of a type of plastic that was fenestrated - meaning that it had small holes enabling oxygen exchange to take place. Now that these lenses are no longer made, increased wear increases the chance of corneal abrasion, irritation, infection, lack of oxygen to the cornea. Be careful with your eyes - they are irreplacable.
If you are going to leave your contact in & sleep with them, please make sure they are extended wear contacts and specifically designed for this purpose. Do not leave and sleep in daily wear contacts as they build up bacteria and material faster and easier than extended wear contacts.
While you eye care professional may prescribe contacts that you can wear up to a week at a time, it is recommended that you take them out every 5 days or so...and then dispose of them (disposable contacts only).
Your eyes need to breath, they do need a break from contacts.
Prolonged use of contacts can leave an impression over the eye...that happened to me.
It depends on the type of contacts you are using. I use a specific type you can even sleep with but my doctor told me not to wear them for more than 48 continuous hours. Maybe this answers your question. The best you can do is to ask your doctor.