Cosinor Online, cosinor on the web, is a simple web-based application evaluating the presence of 24-h periodicity. Loading data is easy, just copy and paste columns from an Excel file to the web form.

CoW example
Column one: Time, decimal form. Transform 20:30 to 20.5 etc. If you are not sure how, please, visit this page.
Column two: Values, decimal form. Examples: 2.10, 5, 5.8, 100.2 etc.

Cosinor [Cosine vector] n. A procedure for the analysis of biological rhythms based on the plotting of a cosine wave to the raw data. Note: The single cosinor procedure plots a single cosine function with a presumed period (anticipated on the basis of prior experience) to the time series and provides estimates of mesor, amplitude, and acrophase. More complex cosinor procedures utilize a fundamental function and one or more harmonics.

Refinetti, R. (2016). Circadian physiology. CRC press.