Comanpanies in distress often have to move quickly to ensure the cash flow to ensure a higher selling price. Here the potential buyer can actually make use of the situation as a prolonged DD will add pressure on the target and the price negotiations might change into a positive direction for the buyer.
However, this is of course not very ethical and I would advise any potential buyer to move ahead with the DD as quickly as possible.
The most important DD field in this case would be financial and commercial. First to see the cost structure and then to see the true commercial potential of the target.