SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'ea319898d33d45a39b8ac5beaec11c37b94798314f1cd26ec8146b7848472c51' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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