If you hover your cursor over the date, it shows the full date & time.
For me it says “Apr 7, '99 6:00am”.
(I’m in the UK so that’s British Summer Time (GMT + 1))
It shows Apr 6, '99 10:00pm for me. Which means @Kent_Clark joined barely after midnight his time.
Mystery solved.
Nothing pops up when I hover the cursor over my join date.
Hmm. I just hovered my mouse over your avatar in your post just above this one. Once your summary popped up I hovered my mouse over “Apr 7, '99” and what appeared in a small pop-up is “April 7, 1999 1:00 am”
I’m in the US eastern timezone with DST, so assuming that’s in my local time that would be Apr 7th at 6am in BST where I think you are.
Okay, I hover my cursor over my avatar. Nothing happens. I left click my mouse and a summary comes up.
Posted 35 mins ago
Joined Apr 7, '99
Read 74d (5d recently)
Member Aficionado Anniversary +12 More
I hover the cursor over the date and nothing happens. I left click the mouse and nothing happens. I right click the mouse and I get the usual Back/Forward/Reload etc. stuff.
Then I tried @LSLGuy avatar. Then @running_coach. Then @pjd . Same results. I sense a pattern.
I think @discobot is getting even for all the abuse we’ve been piling on the walking scrapyard.
I did suspect that since it was April 6 in my time zone when you joined, I will always see your join date as Apr 6. Which is screwy.
What sort of weird mutant computer do you have? 
A bog standard Windows PC running Chrome. What sort of weird mutant computer should I be using?
I was wondering if you had a Mac or some linux-y thing. I’m wondering why hover-over isn’t working for you. I’m also a Win10 on Chrome.
Okay, I logged in using Microsoft Edge and I finally see that I signed up at midnight. Except April 7, 1999 was a Wednesday and I know damn well I was not sitting on my computer at home, with its Windows 95 and blazing 56k modem, signing up new accounts when I had to get up in 6 hours and go to work.
That long ago, who knows what time zone logic AOL used, what time zone their servers were set to, and how those things were reflected in the transfer to vBulletin, a bunch of upgrades since, and the transfer to Discourse.
Maybe it was 9pm where you were, but near midnight in AOL’s server facility and when that data got transferred to vBulletin AOL server time as considered to be your local time. Stranger things have happened over 25 years though multiple data migrations in all sorts of IT systems where you;d hope somebody was sweating the details a lot more than SDMB administration ever had the time or skills to tackle.