PaGe missunderstund the RoP-Rule. You can enter enemy territory without RoP. RoP is needed for staying in enemy territory when ending turn. So if RoP is not granted early enough you need to ensure your units leave territy before ending turn. If this is not possible cause a lack of moving points you will be forced to declare war. DoW always gives a "RoP".
There is no need for a time limit. If RoP is not granted before you end your turn, you have no RoP. So you can't let leave units in enemy territy or have to DoW him. So at last the best procedure is to ask before entering territory. Entering without RoP is not directly forbidden. But it may be understood as an unfriendly action.
In this case we should set time limit to reply for RoP offer. Galley often have no choice : stay in the sea or enter to the border. What referee action will be in this case?
There is no need for a time limit. If RoP is not granted before you end your turn, you have no RoP. So you can't let leave units in enemy territy or have to DoW him. So at last the best procedure is to ask before entering territory. Entering without RoP is not directly forbidden. But it may be understood as an unfriendly action.