How can I reduce the delay for real-time filtering?

Dear community,

I have experience in offline (not real-time) processing, and am lowpass filtering an experimental sequence (at 20 samples/s) from an Arduino board. Such filtering reduces the influence of high frequency noise. There is no stopband or cutoff frequency specification, but the temporal delay introduced by the filter should be lower than 300 ms.

1. - How can I reduce the delay introduced by real-time filtering? The filter I am using is a 4th order Butterworth, but other options (such as Savitzky-Golay filter) are allowed.
2. - How can I write a Python/C# code from the filter selected in the previous step?

Thank you all!

Fernando