You can use a CronTrigger if you're interested in calendar-based schedulers (for example every 40 seconds Monday to Friday, or every Tuesday etc) or a SimpleTrigger if you just want it to fire every 40 seconds ad infinitum.
There are plenty of examples here: http://quartznet.sourceforge.net/tutorial/lesson_5.html
This trigger may help you but have a look through the rest of the examples (plenty of them on the web!):
ITrigger trigger = TriggerBuilder.Create()
.WithIdentity("trigger1", "group1")
.WithDailyTimeIntervalSchedule(x => x.OnMondayThroughFriday().WithIntervalInSeconds(40))
.Build();