SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21a0f52f57167495c24bcb7934353ff0a36ae6f91265237199833e0d17903279' 
  AND token = 'D1FSDzFiTbkvh765Bfj3zcj2stRN3gBotIqk381DeYY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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