| 100% | TRIASSIC | 8 | Geological time period of the first dinosaurs |
| 69% | TRIASSIC | 8 | Period of the first dinosaurs |
| 65% | PLEISTOCENE | 11 | First epoch of the Quaternary period in geological time |
| 58% | PERMIAN | 7 | Last period of the Palaeozoic era in the geological time scale |
| 57% | OLIGOCENE | 9 | Third epoch of the Palaeogene period of geological time |
| 55% | YTD | 3 | Period of time from the first day of the year till today: Abbr. |
| 55% | SATURDAYNIGHT | 13 | Time period that can precede the first parts of 20-, 37- and 44-Across |
| 54% | MIOCENE | 7 | First geological epoch of the Neogene period |
| 50% | ERA | 3 | Period of geological time |
| 50% | EPOCH | 5 | Period of geological time |
| 49% | TRIASSIC | 8 | First period of the Mesozoic Era |
| 49% | FUTURE | 6 | Period of time after the present |
| 48% | DEVONIAN | 8 | Fourth period of the Palaeozoic era of geologic time |
| 48% | ORDOVICIAN | 10 | Second period of the Palaeozoic era of geologic time |
| 48% | PERMIAN | 7 | Last period of the Palaeozoic era in the geological timescale |
| 47% | PHASE | 5 | Period of time such as the "terrible twos" |
| 47% | EON | 3 | Geological period of time |
| 47% | EON | 3 | Period of time from the Greek word for "life" |
| 47% | TRIASSIC | 8 | The first period of the Mesozoic Era |
| 46% | BONO | 4 | First Time Person of the Year musician |
| 46% | EPOCHS | 6 | Long periods of time; units of geological time |
| 46% | ONCE | 4 | The first word of a fairy tale, ___ upon a time |
| 46% | HOUR | 4 | Golden ___, period of time before the day ends |
| 46% | JURASSIC | 8 | Period in the Age of Dinosaurs |
| 45% | ERA | 3 | A historically significant period of time, the end of an ___. |
| 45% | ERA | 3 | Stone or bronze age in terms of the time period |
| 44% | MORNING | 7 | The period of time between midnight and noon |
| 44% | MIOCENE | 7 | First epoch of the Neogene Period |
| 44% | ERA | 3 | A period of time, usually mentioned when talking about the past |
| 43% | BALLONE | 7 | Major-league count after the first pitch, about 42% of the time |