by fits and starts

gradual

at intervals fragmentary intermittent interrupted little-by-little partial patchy spotty step-by-step

erratically fitfully haphazardly infrequently sporadically unevenly

any which way anyhow at intervals by turns disconnectedly eccentrically helter-skelter in snatches jerkily now and again occasionally off and on out of sequence periodically slapdash spasmodically uncertainly uncommonly unmethodically unpunctually willy-nilly

evenly regularly