To answer your question, normally less than an hour.
I am guessing you have a Gmail address. Look for it in your Spam folder. Nearly identical emails such as auto-responders are mostly filtered to there because gmail sees the nearly exact thing being sent to many people and flags it as a trend.
If you have another email provider, you may want to check what active filters they have. Or, add "@solidworks.com" to approved senders list or something like that. I don't know the actual domain of the activation code email that you're looking for so that you could whitelist the correct one.