I tried using the kaud's suggestion, as there was a log output ..

The log format looks some what like printf/scanf format from c:
LogMessage(false, true, "%s Date File : %s. Compression = %.0f%%%", loadsave, per.GetFileName(), flRatio);

So I tried to convert the output to long double
LogMessage(false, true, " PRIYA file save took : %lf", std::chrono:uration<long double, std::milli>(diffr).count());

Im getting value of 5064.434000 ms. Not sure if i used the %lf properly .. Because there is possibility of overflow errors etc

Please comment and kindly help me