SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b92de6d8e370185120ed8ce18a53742262767346083b447c252bc84dfb546e31' 
  AND token = 'xAwDWaVFud4nPY2LrOqpVsqDpJAXg3avxVxi+cAdHI4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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