SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '44ca887c661210b4ea838c32db15a428fecb50baa1b223561754db999c1209a4' 
  AND token = '3aIXEcccDUQVbph8ErySWWSaD7zwGYb1HhA0RQYVjpY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00036

JSON explain

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