For Exact text match in regular expressions

add '^' in the beginning of the expression and '$' at the end of the expression
syntax: ^$
e.g. ^\d\d:\d\d:\d\d$

if this didn't work out

try using '\b' in beginning and the end of the expression
syntax: \b\b
e.g. \b\abc\b

Random Double number within given range in c#

double NextDouble(Random rng, double min, double max)
{
return min + (rng.NextDouble() * (max - min));
}