every so often

annual intermittent monthly occasional recurrent recurring regular repeated routine seasonal sporadic weekly yearly

periodical

alternate at various times centennial cyclic cyclical daily epochal every once in a while fluctuating hourly infrequent isochronal isochronous on certain occasions on-again-off-again orbital perennial rhythmic serial spasmodic

constant infrequent unusual

continual irregular lasting permanent sporadic variable

from time to time now and again occasionally on occasion once in a while

at times ever and anon evermore from time to time now and again now and then occasionally on occasion

now and again now and then

ever so often every once in a while from time to time once and again once in a while sometimes

occasionally periodically sporadically

again betimes from time to time now and again on occasion once in a while sometimes

every now and then 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 once or twice sometimes

hardly infrequently periodically seldom sometimes sporadically

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

always constantly frequently regularly steadily usually

alternately at intervals at times every once in a while fluctuating from time to time irregularly now and then occasionally on occasion once in a while sometimes sporadically vacillating variably

at intervals at times discontinuously every now and then every once in a while from time to time hardly infrequently intermittently irregularly now and again now and then occasionally off and on on occasion once in a blue moon once in a while periodically sometimes sporadically

every now and then from time to time infrequently irregularly now and again now and then occasionally once and again once in a while periodically sometimes sporadically

at intervals at times every now and then from time to time hardly infrequently irregularly now and again on occasion once in a blue moon periodically rarely seldom sometimes sporadically

consistently constantly frequently occasionally

at intervals at times ever and again from time to time here and there intermittently now and again now and then off and on on occasion once in a blue moon once in a while periodically recurrently

never