In the timesheet mode, you need to define separators with the date of the first row (i.e., add the specified hour to the first day):
const timesheet = new DayPilot.Scheduler("scheduler", {
viewType: "Days",
startDate: DayPilot.Date.today().firstDayOfMonth(),
days: DayPilot.Date.today().daysInMonth(),
separators: [
{color: "red", location: DayPilot.Date.today().firstDayOfMonth().addHours(2)}
],
// ...
});