SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'f349ac526606d5f123692fa2fa30a5adcb358cc2149a58c65b43b7e4a2160ea2' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00016

JSON explain

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