Covid Insurance minimum period requirements

I know about the USD50k coverage requirement for covid when entering the country.  However, is there a minimum period this must be for?  For example, if you are coming in on a 3 month non-immigrant visa, do you require the coverage for the full 3 months or just 1 month, i.e. enough of a period to clear your "risky" arrival period.  I've read other readers post that they have normal travel insurance from the UK but this doesn't meet the specific covid requirement as it doesn't specifically state covid.  

I could be wrong but I think they are trying to encourage you to buy the policies from Thailand for people based in Thailand who are returning home but plan to come back to Thailand.  I could be wrong....  Bit like the PCR tests which are very expensive here and much cheaper in more expensive countries....somebody is making money....

I have Thai social security with my job if that makes any difference at all.