Return timestamp (number) representation of Position,Duration besides String

[kenkangxgwe]

Return a number representation of Position and Duration for [MeasurePosition:] according to https://docs.rainmeter.net/manual/variables/section-variables/#Colon.

This will be useful to

1. calculate the remaining time: ([MeasureDuration:] - [MeasurePosition:]).
2. customize the format by UpTime Measure: https://docs.rainmeter.net/manual/measures/uptime/#SecondsValue.