What does %FS (Full Scale) represent in load cell?
If full-scale is 12 mV then 0.02% of 12 mV is 2.4 μV.

100%  = 12000 μV
10%   = 1200 μV;
1%    = 120 μV
0.1%  = 12 μV
0.01% = 1.2 μV

So after 1 minute, you might expect a reading of (say) 1 mV to creep to 1.0024 mV or 0.9976 mV.