If the box "I have no intention at present to remarry/enter into a new civil partnership or cohabit" is ticked on form D81, is there a time limit on this and if one of us does cohabit, etc in that time limit (if there is one) are we breaking the regulations of a court order??
There is not a time limit per se. Whether a person has an intention to cohabit or remarry goes to the question of their needs in relation to dividing finances/assets. If a spouse intends to cohabit or remarry then their needs could be reduced and this could impact on the division of assets. Particularly in a small asset case, where needs are important it could mean receiving a smaller share of the assets.
So if someone, says they have no intention, then cohabits/remarries within a short period of time, it leaves the door open for the other party to apply for the order to be set aside. Whether this would be successful is dependent upon the facts of each case.
The brief answer would be if you do intend, then say so. If you believe the other party intends, and they say no and the order would be different if they did cohabit/remarry, then put something in the recitals of the order saying that the other party has no intention of...., and the order has been agreed on this basis.