No, it is not possible for the entire planet to experience time dilation without us noticing. Time dilation occurs when there is a difference in the passage of time between two reference frames that are in relative motion or are in a gravitational field.
If the entire planet were experiencing time dilation, it would mean that the passage of time on Earth would be different compared to the passage of time in the rest of the universe. This would have significant observable effects, such as discrepancies in the rates of clocks and the behavior of various physical processes.
Time dilation has been experimentally verified and is a well-established aspect of relativity. It is taken into account in various scientific applications, including satellite navigation systems, particle accelerators, and precision timing experiments. If the entire planet were experiencing time dilation, it would have profound consequences that would certainly be noticeable through careful measurements and comparisons with other reference frames.