Once you download and install this Right Inbox tool your compose message Window has two more buttons. One called Schedule and another called Track. Schedule permits you to specify a date and time for dispatch. Track helps you know when the message has been opened; You will also know, if there is a hyperlink inside your message, if that was clicked. Tracking tells when, where (city & country) and from which IP address it was accessed. It is almost a spy!. A link to Map showing the place of opening the message is also available.
This is a very useful application. May be used in critical messages where you want to ensure delivery and acknowledgement. Some bosses bluff that they have not yet seen your mail or lie that there were on a tour etc. You can not of course show the acknowledgement / tracking message and annoy him further!
The free version has all the facilities and features but you can only schedule and track up to ten messages per month. Purchased versions are more liberal.
While scheduling I have noticed a small problem. If you set the country standard for time (say: IST = GMT +5.50 hrs) from within the schedule window there could be some problem. Time standard is best set at Chrome level. When a message is scheduled to be sent at say 17:30 the time stamp of the message is set to 17:30 but actual delivery may be later depending upon queue and traffic flow.
I do not know why Gmail was shy of providing this facility despite many users asking for it.