SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '2c34c39a6fbb10a9921e90cf53fbeb4709a815e6d39c34110d3c0145dd1db622' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00015

JSON explain

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