[tialaramex]

In a performance language your "real types" aren't somehow more expensive and so you should only use the built-in primitives when they accurately reflect your intent. So I would write:

time += Duration::from_millis(1);

But I would expect that "time unit should be in the variable name" is a reasonable choice in a language which doesn't have this affordance, and I needn't care about performance because apparently the language doesn't either.

I also wonder why we've named this variable "time". Maybe we're a very abstract piece of software and so we know nothing more specific? I would prefer to name it e.g. "timeout" or "flight" or "exam_finishes" if we know why we care about this.