How much Due Dilligence time should i put into an offer

[Tom Knox]

I am looking at a 3plex (in a not the best area) and the numbers are working out for me so far. I have given the seller a low offer which they immediately rejected and came back with their original asking price as well as a 5 day Due Diligence period. I will be financing this property and am unsure if this time period is realistic or not. The property will cash flow at asking price but there likely won't be any appreciation accumulation for the property for a long time.

My question: Is a 5 day due diligence period unheard of? What is a normal due diligence time period (This would be a buy and hold property)

Thank you in advance