When trying to ascertain why timestamps seem to disagree with each other, it is often important to start with an accurate (as possible) timeline of the events being reported on
It is also helpful to keep things co-ordinated to a single point of reference with respect to time, so we'll use UTC.
Timeline
- FDB981 Scheduled to arrive Rostov-on-Don at 18th March 22:20 UTC (local: 19th March 01:20 MSK )
- First approach aborted at 18th March 22:42 UTC (local: 19th March 01:42 MSK)
- Second approach begins at 19th March 00:28 UTC (local: 03:28 MSK)
- ATC alerts emergency crews of the crash at 00:42 UTC (local: 03:42 MSK)
(Note, the above is taken from the wikipedia article on the air crash As timings are rarely contentious, these figures are taken to be accurate.)
Videos
Two YouTube videos are under question, with both having descriptions ostensibly time stamped 18th March.
Helpfully, Amnesty International maintain an Youtube DataViewer which can extract the actual upload time of videos on you tube.
The first video has this description (auto-translated)
Published on Mar 18, 2016
Today March 18, 2016 in the 3-50 MSK at the airport of Rostov-on-Don arrived from Dubai crashed aircraft "Boeing 737-800". At an altitude of approximately 100-200 meters of the aircraft it took to complete the so-called peak and almost at a right angle at high speed crashed into the ground. 50 of the 55 passengers on board were Russians, five others - citizens of Ukraine and, presumably, Uzbekistan, all seven crew members were foreigners. Survive could not be anyone of them.
Using the DataView tool, gives the following information:
Video ID: oSzFPvG6EJM
Upload Date (YYYY/MM/DD): 2016-03-19
Upload Time (UTC): 06:24:31
The second video which has the identical description reveals:
Video ID: e_UFhwRVY1I
Upload Date (YYYY/MM/DD): 2016-03-19
Upload Time (UTC): 04:37:50
Russian Wikipedia
A cursory look at the revision history of the Russian Wikipedia page shows the earliest revision to be 19th March at 03:34 UTC. Again, this was many hours after the reported crash.
Conclusion
It is pretty clear that the two videos in question were uploaded, and the Russian wikipedia entry created, roughly 3-6 hours after the crash of FlyDubai 981.
It is quite possible that the user who uploaded the videos incorrectly noted the date. It is also worth remembering, that as the incident occurred just after midnight UTC, roughly half of the world was still on the 18th March. Without knowing the location of the video uploader, its possible that they were reporting on something which actually happened on the 19th March, whilst they them self were still in the final hours/minutes of 18th March.