seven o'clock
We must be careful , girls . '' `` It 's getting darker , '' observed Betty . `` We must be quick Mollie , if we 're to get to shelter before the storm breaks . '' It was growing dark and gloomy , and though it was not yet seven o'clock the lowering clouds had added to the dusk of approaching night . Occasionally , in the distance , could be heard the low rumbling of thunder . `` Oh dear ! '' exclaimed Grace .