Describe the bug
If an input cube only has a single value for the time, clip_timerange removes this and demotes the time coordinate to a scalar auxiliary coordinate. This causes some NCL diagnostics to fail (https://esmvaltool.dkrz.de/shared/esmvaltool/v2.5.0-test-rc2/recipe_anav13jclim_20220216_162114/run/diag_two_vars_scatter/scat_global/log.txt).

Please attach
main_log_debug.txt

File before clip_timerange:

netcdf \02_cmor_check_metadata {
dimensions:
        time = 1 ;
        lat = 192 ;
        lon = 288 ;
        bnds = 2 ;
...

After clip_timerange:

netcdf \03_clip_timerange {
dimensions:
        lat = 192 ;
        lon = 288 ;
        bnds = 2 ;
...

I will try to come up with a fix for this.