Every 2 seconds:

new Schedule(() => { /* your code */ }, run => run.Every(2).Seconds());

Once, after 5 seconds:

new Schedule(() => { /* your code */ }, run => run.OnceIn(5).Seconds());

Now and every 5 minutes afterwards:

new Schedule(() => { /* your code */ }, run => run.Now().AndEvery(5).Minutes());

Every weekday:

new Schedule(() => { /* your code */ }, run => run.EveryWeekDay())

Every weekend:

new Schedule(() => { /* your code */ }, run => run.EveryWeekend())

Everyday at 21:15:

new Schedule(() => { /* your code */ }, run => run.Every(1).Days().At(21, 15));

Every 20th on the month:

new Schedule(() => { /* your code */ }, run => run.Every(1).Month().On(20))

Everyday except Mondays:

new Schedule(() => { /* your code */ }, run => run.Every(1).Days().Except(DayOfWeek.Monday))

Everyday between 01:00 and 04:00:

new Schedule(() => { /* your code */ }, run => run.Now().AndEvery(1).Days().Between(1, 0, 4, 0))