SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '39ea6435083b2b84818374e4999006a8aff50dab0db14cb537cbe559c31e0637' 
  AND token = '17PS+6GpsMw3oEMLlwKKddxSXfbaZCE8ae8KMuzw6nk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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