once or twice

every now and then every so often infrequently intermittently now and again occasionally periodically sporadically

at intervals at times every once in a while from time to time hardly irregularly not often off and on on occasion once and again once in a blue moon once in a while sometimes

hardly infrequently periodically seldom sometimes sporadically

at intervals at random at times every so often from time to time irregularly now and again on occasion once in a blue moon once in a while uncommonly

always constantly frequently regularly steadily usually