DateTime in Microseconds

There are two separate logical operations here:

• Converting from ticks to microseconds. This is basically a matter of dividing by 10 (there are 100 nanoseconds or 0.1 microseconds in each tick), so that can lose information already in integer arithmetic - but adding 50 ticks is adding exactly 5 microseconds, so that should be okay.

• Converting from an integer to a binary floating point number. Your value has 17 significant decimal digits, which is on the higher end of what a 64-bit binary floating point type can represent. You shouldn't rely on more than 15 significant decimal digits.

On top of that, you're using ToOADate, which appears to have millisecond precision, looking at the reference source.

So:

• You could just divide Ticks by 10 to get microseconds, only losing a small amount of precision
• You could convert from long to double in a different way, which would lose less information than ToOADate but you're still going to be losing information in many cases.
• If you divide by 10.0 (so avoiding the integer arithmetic to start with) then depending on the value you're trying to represent, you could avoid losing any information.

If you are able to choose a different epoch for your double value, you could easily express microseconds in values with appropriate precision - but you'd need to know the range of values you need to express in order to check that, as well as having control over the rest of the code using the resulting double values.