login/update_logon_timestamp is a SAP Parameter attribute which is used to control update frequency / accuracy of logon timestamp information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
A timestamp (date/time) can be created with each logon. For performance
reasons you may want to reduce the refresh rate of the required
accurateness: For instance, it may be sufficient to only refresh the
timestamp if the minutes have changed.
The required accurateness and refresh rate can be changed with this
Allowed Values d - exact to the day h - exact to the hour m - exact to the minute (default value) s - exact to the second (backward compatible)
See SAP Parameter Documentation for full SAP documentation for this profile parameter.