I am assuming that the Secret Service has a schedule of events of their protectees and update it as it changes. Even if President Trump didn't have a golf outing on his schedule for Sunday, the SS would have just needed to implement their usual plan for when there is a golf outing there, once they were informed that an impromptu golf outing was planned. President Trump had a rally in Arizona the night before and probably got back pretty late Saturday night/Sunday morning or even may have returned on Sunday morning and since he had a special guest with him from NYC, they decided to play a round of golf. One would assume that the SS would just implement their plan to sweep the course that they always do when they are protecting President Trump on a golf outing, even if it wasn't scheduled in advance. There would be procedures already in place that they could implement. I didn't hear Rowe say that they didn't have time to implement their procedures.
There also is no evidence that I have seen in MSM anywhere that suggests that the Secret Service ever asked President Trump not to golf on his golf course and suggest that he go to some other golf course in the area, although there is some speculation that they have done so and that President Trump ignored their advice. Purely speculation as far as I can tell.
Sweeping an 18 hole golf course probably takes quite a while. If Trump was impatient to play anyway, they may have had to improvise the plan to let him play while the SS agents went sweeping hole by hole, ahead of Trump. It's always a dilemma for SS agents when they have to deal with protectees who want to bend the rules. That's been the case through many, but not all, administrations. I think I recall some of Gerald Ford's kids liked to sneak out at night. Bill Clinton liked to go out jogging, then take off for the closest McDonalds. Bobby Kennedy and his brother JFK were always jumping out of cars to shake hands with voters on the streets, etc.