SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '721edb8187b8f745269354a49f989394216f35d67915e21aa0189f5874a6e1e6' 
  AND token = '/+HgrDRzEvE73YHKfZ5LIHl/3zyG7CziL6C0+q9NWlY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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