I'm assuming that your joint means that the worktop needs to be crosscut to one side or other of the cut-out in which case I'd say leave at least 300mm if at all possible - less and you may find that the top cracks if someone hops up onto the worktop. In any case you'll need 150 to 200mm to accommodate the joiners and leave clearance to get at the hob clips, ets. If nothing else it's good practice to locate a hob with worktop space either side if you can.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local