Start of time range limit to serve.
Thanos Store serves only metrics, which happened later than this value. Option can be a constant time in RFC3339 format or time duration relative to current time, such as -1d or 2h45m. Valid duration units are ms, s, m, h, d, w, y.
Defaults to 0000-01-01T00:00:00Z in Thanos when set to null.