Here it is, the golden elixir 
Just kidding. This is the promised update, [I know, I know, promised long ago… yada yada.. I am sorry].
Its labelled version 1.2.0.0 and includes MANY new features:
- Improved – Background polling now does not consume many resources since it only looks at headers
- Improved – Header search and replace is more consistent across platforms
- Fixed – Many minor crash issues and formatting issues [from beta]
- New – 3 configurable buttons with preset [configurable] time offsets
- New – Keyboard shortcuts to preset buttons [ALT + 1, ALT + 2, ALT + 3]
- New – Send Later Toolbar available
- New – Send Later header visible in drafts folder [configurable]
- New – Send Later column visible in drafts folder [configurable]
- New – AwesomenessÂ
Send Later 1.2.0.0 Prompt Screenshot – 3 Quick access buttons that can be configured as you like, with shortcut keyboard access using ALT+1,ALT+2,ALT+3
Send Later 1.2.0.0 Preferences Window – More preferences for people who like to tweak things till they are perfect
Send Later 1.2.0.0 Configurable buttons- And the quick access buttons are configurable as well
So how do you get this awesomeness ? If you are already using a previous version, Thunderbird should prompt to update from this website, so you should be covered or you can try Tools -> Extensions / Addons [Right click and choose find update]. If you want to install it afresh then you can download it from here.
BTW, Send Later got featured in quite a few websites over the last couple of years and its time to thank them.
Send Later is download of the day on Lifehacker
Send Later is one of 10 must have extensions for Thunderbird
Watch out for more progress on this. If you have any troubles drop in a comment below and I will sort it out.
Regards
Karthik