Avoid duplicate times cdo mergetime

I'm trying to merge NetCDF files with ncrcat:

ncrcat drycblles.default.000* drycblles.default.nc
This works fine, unless some files have overlapping times, in which case I get time records like this:

t = 0, 300, 600, 900, 1200, 1500, 1800, 2100, 2400, 2700, 3000, 3300, 3600,
3900, 4200, 4500, 4800, 5100, 5400, 5700, 6000, 6300, 6600, 6900, 7200,
3900, 4200, 4500, 4800, 5100, 5400, 5700, 6000, 6300, 6600, 6900, 7200, ...

CDO has an option to remove duplicate records with e.g.

export SKIP_SAME_TIME=1