"He buys into the package that anything less than promotion is failure," Scally told BBC Radio Kent.
"We'll be aiming for top three and we want everyone to buy into that concept. Anything less than promotion back to league one will be disappointing."
Hessenthaler starts work on Monday having left his job as manager of Blue Square South Dover Athletic on Thursday.
Mark Robson, who coached under Stimson, is promoted to assistant manager and one of his first tasks will be to decide which of the 13 out-of-contract players will stay.
But Scally denied that Nicky Southall is returning to the club, either as player or part of the coaching set up.
He also rejected that he had approached Hessenthaler before he left Dover just a day before his appointment.
"I spoke to Andy on Thursday afternoon and as a result of that conversation I asked him to come out to Dubai straight away which he did."
"It all happened very quickly. I got him onto a late flight with Mark Robson. We spoke for about four or five hours and we made the appointment. They're absolutely right for the football club."
Source: BBC Sport
Source: BBC Sport