SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b526e523cb561f2608fe29a9aa76895ed36299fd6769b2f0ea5a8aaf992c4874' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}