If the filtered list of where clause returns you a comma separated list ALWAYS, you can do something like:
countryRestApi.data.where('name', country.value, '==').utctimes.split(',')
countryRestApi.data.where('name', country.value, '==').values('utctimes').split(',')
But, if that is not the case, you will have to create a custom formatter in JS which will read each of the rows in filtered data, and create a new array of items from that. Resulting in a merge single list of all filtered rows & their multiple comma separated value.