Adding a results query to drop dynamic initial values into a list selector (instead of relying on 'pick initial values' setting in edit mode of a dashboard

So client wants 2 snapshot dates populated . Snap1 is the most recent snapshot--easy enough to accomplish by a query sorted in ascending order which takes the most recent one and puts it in snap1list selector. The 2nd snapdate is 1 year back. This can be done by populating the 'start' attribute in dashboard JSON with a results from query 'q_oneYrBack_1'.
    "start": "{{cell(q_oneYrBack_1.result,0,\"sd2\").asString()}}"

 "q_oneYrBack_1": {
                "broadcastFacet": true,
                "groups": [],
                "label": "q_oneYrBack",
                "numbers": [],
                "query": "q = load \"zds_completeOpptys_v2\";\nq = filter q by date('SnapshotStamp_Year', 'SnapshotStamp_Month', 'SnapshotStamp_Day') in [\"365 days ago\"..\"365 days ago\"];\nq=  group q by 'SnapshotStamp';\nq = foreach q generate 'SnapshotStamp' as 'sd', substr('SnapshotStamp',2,10) as 'sd2';",
                "receiveFacetSource": {
Sd2 resolved to text in yyyy-MM-dd format (hence the 10 character string in the substr function).