Something like this would indeed be a nice feature to add to Messenger Plus! itself. But don't get your hopes up too much though.
Adding it via a Messenger Plus! script is what is currently being done by Matty (but again, this is done as one of his many side projects, so don't expect it to be finished tomorrow). But note that because of the way scripts are run, they can not do everything what other plugins (like StuffPlug) did.
Setting the proper times and settings would be done like in any other script: either via a command or via a settings dialog or both.
As for the position of the time: under the display picture would be nice, yes. But that is as good as impossible with scripting; it certainly is not the simpliest, no matter what form of tweaking tool (script, plugin, etc) you use.
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Note: to make something like this in a proper way, you also need a pretty advanced way of selecting the proper timezone per contact.
It is by no means as simple as setting the hour difference between you and the contact!!!!!
This because of the many different DST rules around the world. DST rules are difference per timezone and even per region (they are actually independant of timezones) and they even change from one year to the other for some or even more frequently. They are also not applied at the same time around the world. Note that even Windows itself does not get it right for all regions in the world.
To give an example: the most advanced and correct clock/timezone widget for Windows I've ever found is
Anuko World Clock. This gets updated almost every month and almost each time it also includes an update for its timezone and DST rules database (usually this is for more exotic regions though, but it isn't always).
To give an example of how complicated things will get with DSTs: Recently the Palestinian Authority in Ramallah and Gaza have decided to end DST during Ramadan and also Egypt cancelled DST during Ramadan only to resume it again after Ramadan. Bahía de Banderas (Mexican state of Nayarit) changed its timezone (UTC-7) to the new time zone UTC-6 on April 4, 2010 to share the same timezone as nearby city Puerto Vallarta, Jalisco. San Luis, Argentina (UTC-4) will keep DST after April 11, 2010; it will continue to have the same time as rest of Argentina (UTC-3), thus no DST.
And the list goes on and on and on on a monthly, sometimes even daily, basis. And as you can see, not all of them are stricly for exotic places.
Als note that while the general rule for applying DST is to set the clock one hour ahead, there are again exceptions. Like Lord Howe Island, Australia, where the clock is advanced only half an hour during DST.
Another important note is that the time offsets (eg: UTC-3) aren't always an integral number either! In some places the difference is half an hour or even a quarter hour (eg: Nepal which is UTC+05:45)
All this just to say that simply setting the time difference between you and your contact by selecting some integral number between 0 and 12, like you will find in so many tools which offer some time display, is in no way accurate and absolutely incorrect and insufficient.
And then there is the other problem of what to do when your contact actually travels around the world. Then your settings for that contact wont be correct anymore either... But that is an entirly different problem (which could partially be solved, together with the DST problem, by getting the time from the contact itself though)...
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