The Dutchman is keen to revamp the playing staff he inherited from predecessor Roberto Martinez in the summer and will use the next two transfer windows to strengthen, while also moving on players who do not fit into his plans.
"We know that due to the people we have inside the club that this is a project which is for the long term and it does not mean that you are fighting for trophies within six months of arriving at a new club," he told Dutch broadcaster NOS.
"We need to invest not only in January, but also in the next summer transfer window.
"I believe that the club are aware of this and that I will receive the time. But it is not easy to get time within football these days."