I'd prefer if this were done with two inputs instead of constructing the query string manually. Like in the lines above: https://github.com/prometheus/prometheus/blob/1f484b03c78fb519c1b6da3c05a2c482e42f5455/web/static/js/graph.js#L235 - one visible entry field ("end_input") for the human-readable value and a hidden field with the computed value ("end").