at intervals
now and again; intermittently
Your system was liable to periodical convulsions...business crises at intervals of five to ten years, which wrecked the industries of the nation. Edward Bellamy
I had to decide [he said later] whether I would be a lawyer by profession and a revolutionary at intervals, or a revolutionary by profession and a lawyer at intervals. Eleftherios Venizelos
A person needs at intervals to separate himself from family and companions and go to new places. He must go without his familiars in order to be open to influences, to change. Katharine Butler Hathaway
Stations were built at intervals averaging fifteen miles apart. A rider's route covered three stations, with an exchange of horses at each, so that he was expected at the beginning to cover close to forty-five miles - a good ride when one must average fifteen miles an hour. Buffalo Bill
The modern young man,' said Aunt Dahlia, 'is a congenital idiot and wants a nurse to lead him by the hand and some strong attendant to kick him regularly at intervals of a quarter of an hour. P. G. Wodehouse
I woke at intervals until . . . the intervals of waking tipped the scales, and I was more often awake than not. Annie Dillard