from datetime import time
import time

last_ts = time.time()
iterations_threshold = 1000000
num_iterations = 0
for item in ...:
    num_iterations += 1
    if num_iterations % iterations_threshold == 0:
        curr_ts = time.time()
        print(f'{datetime.now():%Y-%m-%d %H:%M:%S} '
              f'({int(curr_ts-last_ts)}) {num_iterations}')
        last_ts = curr_ts