SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '03a55fd9674fd9cd0a1b544322846d046a6c7a50709d95a725473bde6f9e1568' 
  AND token = '31kGkildnCQuGf188+iE1FjYkrM/wJZLaD6UjxaNi+g=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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