dataset: The source dataset, in dataframe format, which needs to be marked.
timestamp: The column name in the dataset that will be used as timestamp.
startTime: Define the starting time of a day. It must be in the format of "hh:mm:ss".
tz: Local time zone, defaults to UTC.
Returns
A dataframe with an extra day marking column.
References
Choi L, Liu Z, Matthews CE, Buchowski MS. Validation of accelerometer wear and nonwear time classification algorithm. Med Sci Sports Exerc. 2011 Feb;43(2):357-64.