SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '39ea5f7273921d3f256b65ca42aafab64d8abb73fc5de91f2932aceea603d357' 
  AND token = 'DFTz+rptNvibGpZUF96i3XzEwkSK9z9+YIncYDBanyw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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