SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'bc8fa5cbdc6e0b551d26ab0398390a89ceb0a43ee39e827f3cf375b525c71f51' 
  AND token = 'cLDAqDJ8K+ywQgQAWmakGX5xVQIJTjgOutKQhjBoJRc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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