Convert SysTime to TickDuration?

[Andrej Mitrovic]

I'm trying to port some Tango D1 code to D2, I don't know why ticks
are used, but this was the code:

timeModified = Path.modified(path).ticks;

It fetches the modification date of a file and apparently converts
that to ticks. I've tried using Phobos' std.file.timeLastModified
which returns a SysTime, but I don't know how to convert that to
ticks.

Anyway, if that's not possible I'll just have to rewrite more code,
it's not too big of a deal.