SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51f42e207f929ef55c2dd7fc96d30a5e76b67d49b0a7462aaca28cd31c67129c' 
  AND token = '9/pIaTeLyYL6PLxYws5gBP6N+DOlnnedwdENEgOi2Xg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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