Quartz.Net tutorials are mainly based on Quartz.Net v1.
If you are using v2 +, you can use the following trigger definition:
ITrigger trigger = TriggerBuilder.Create()
.WithIdentity("trigger1", "group1")
.WithDailyTimeIntervalSchedule(
x => x.StartingDailyAt(TimeOfDay.HourAndMinuteOfDay(8, 0))
.EndingDailyAt(TimeOfDay.HourAndMinuteOfDay(11, 0))
.WithIntervalInMinutes(45))
.Build();
, 45 , 8:00 11:00.