The Scottish manager joined the Phobians in a two-year contract last month, and has been tasked with ending the club's seven-season run without a major trophy.
''We have a two-year contract with him and he has just begun his work. We need to give him time. He is getting to know the players,'' Nelson told Starr FM.
''There is a target for him but it doesn’t mean that if he fails to win the league title he will be sacked. That is not part of his contract.
“We are giving him all the support he needs and we know he will succeed with the club. There is still a long way to go in the league and anything can happen," he added.
Hearts will lock horns with city rivals Great Olympics in the Accra derby on Sunday.