The start time displayed changes every time I insert a marker

Temprecord calculates the time of the first sample displayed on the summary tab by taking the current time and counting backwards, using the number of samples taken and the sample period. If the sample record contains markers as well as temperature values, the start time will be earlier by the number of markers multiplied by the sample period if the data has not been read from the logger.

Thus if there are samples with markers in the logger, the time of the first sample in the logger will be earlier than the true value.

The time that is annotated First Sample in the summary display is the time of the first sample in the logger. If the logger is not overwriting, this corresponds to the time the logger took the first sample after it was started, but if the logger is overwriting, it corresponds to the time of the earliest sample in the logger. Every time the logger takes another temperature sample and stores it, the oldest sample is overwritten and lost, and the time of the first sample will advance by one sample period.

The time that is annotated Time Logger Started on the other hand, is the time the very first sample of the trip was taken. If the logger is overwriting, this sample is no longer available.