To add to this:
I expect these observations are made 2x per day at 0000UTC and 1200UTC. The correct declaration of the coverage is then 00:00 to 23:59 (covering the whole day) with an interval of 12 hrs. Assuming these observations are reportedly immediately after generating the data, the reporting interval is also 12 hrs. Depending on how long it takes for the data to actually become available to a user, you could also declare a latency of reporting. Please consult the Figure 2 in the WMDS document for an illustration.
Kind regards
Jörg