The Boro programme the last 2 matches said the Monday. So it definitely was originally on that day.The EFL page at https://www.efl.com/news/key-dates/ was crawled and archived by the waybackmachine
The dates it was crawled is available here: https://web.archive.org/web/20230000000000*/https://www.efl.com/news/key-dates/
the links to the page as it was archived are here:
10th August 2022 https://web.archive.org/web/20220810225126/https://www.efl.com/news/key-dates/
29th September 2022 https://web.archive.org/web/20220929134054/https://www.efl.com/news/key-dates/
29th November 2022 https://web.archive.org/web/20221129234511/https://www.efl.com/news/key-dates/
25th December 2022 https://web.archive.org/web/20221225065542/https://www.efl.com/news/key-dates/
1st January 2023 https://web.archive.org/web/20230101024934/https://www.efl.com/news/key-dates/
24th January 2023 https://web.archive.org/web/20230124212305/https://www.efl.com/news/key-dates/
15th March 2023 https://web.archive.org/web/20230315141600/https://www.efl.com/news/key-dates/
I think that on all those dates the playoff finals were shown as being over the weekend without specific dates for each of the the three matches. Of course this doesn't mean that this page did not show different information on other days that it was not crawled by the internet archive.
And of course other websites, such as clubs, could have shown different information.