A "time stamp" only marks a point in time, you can use words meaning "today", "on Monday", "in 2 years", etc. But in {DIS law'} you are not talking about a reference point in time, but about a long duration during which you did something. So {qaStaHvIS ...} is the correct option.
Now you might argue that "in 2 years" and "(during) many years" both refer to quite broad time spans and not necessarily to *points* in time, but for "in 2 years" there is no duration specified, while "many years" explicitly refers to a duration.
{ben law'} 'many years ago' would stand alone without a {qaStaHvIS} before it.