When you send a smart campaign to yourself, you can be sent, receive and click the email in less than 2 minutes. I think that this is not enough to characterize a bot in fact . Suffice that you send the email to someone who is not doing anything else that sorting and browsing through emails. A bot would have multiple clicks in the same duration.
If a bot is handling it, the 2 events will occur in a very short time. But they are registered in Marketo through 2 very different mechanisms:
The timestamp recorded in Marketo therefore depends mainly on factors such the Internet latency (for the image download or the click detection) and the speed processing it in Marketo infrastructure.