SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b6c1c29ec9526f57200c4792315a481e0de1aff3659e87490469eca77109420e' 
  AND token = 'eK5bT5lTiFpYTbmKGvCyrjJCASYdJisHCzFWn//hqTs=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00037

JSON explain

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