Optimal time and flow rate strongly depends on the geometry of the cell and, in particular, on the form of gas outlet. As Cornel Radu mentioned above, small gas bubbles are more efficient, so do use glass frit at the outlet. To my experience, indeed, from 5 to 15 mins of moderate purging is enough. Blanketing is indeed very good strategy to make an experiment in stationary but protected electrolyte. For blanketing, I found Ar is more efficient than N2, as it is heavier.

A purging time of 5 min is enough for 15-20 mL solution, if the bubbles are very small and you maintain the blanketing (the gas flow is maintained below the cell cover, without purging). The flow is good enough if you see separate  small bubbles (use a porous frit).

Optimal time and flow rate strongly depends on the geometry of the cell and, in particular, on the form of gas outlet. As Cornel Radu mentioned above, small gas bubbles are more efficient, so do use glass frit at the outlet. To my experience, indeed, from 5 to 15 mins of moderate purging is enough. Blanketing is indeed very good strategy to make an experiment in stationary but protected electrolyte. For blanketing, I found Ar is more efficient than N2, as it is heavier.

Purging time and flow rate entirely depend on the how critical oxygen affects the result. Generally, 25 min purging (small bubbles) is sufficient enough to remove the dissolved oxygen in  25 mL solution.