Analog filtering for very low frequency signals

[Ken Smith]

If you use an IIR filter the system delay won't be much more than an
analog filter (the filter itself will be comparable, any excess will
just be from the acquisition and output sample time).

Actually the delay may be less in the digital case. With real analog
parts you may need to put in more poles to make up for component
tolerances. In the digital IIR version your parts can easily be good to
0.1%