SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51601ab54401d1cafa8c8443d7de51b505669281bc510430a58a7f959f9fa984' 
  AND token = 'gkLTC9upz8nZmBGBwzAVoIOjP3bpMqBFaDQ4+65rrc4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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