SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '876f80b77b291325ced2668e495dca1a945607b8f8c18101a70705553a02275c' 
  AND token = 'ZmSUh4/TL7v1zD8uTKJSxIlJVovaBSzCwvE5l0/3sCw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}