SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6fe571e0447c19acc28233564572e7ce146e623e9432adbfcdd7b7dca1c85c15' 
  AND token = 'lU3XqwMdrqEwE6KRTRj+KKxevjm6aPSpeTDa6D/GCQ4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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