Sync your Clock
Make 100% sure you set this up when using Sierra Chart!

Does my PC clock need to be synchronized?

Yes it does. The last thing you want as a trader is issues of any kind while trading live. You better be aware of your full risk spectrum and this technical issue is part of that.
A difference between your local computer clock and any trading service you use can result in unexplainable issues when trading live.
When you start Sierra Chart your message log will also show a message when your hardware clock isn't synchronized and by how many seconds.
I know that SC message log says a lot of things and you are not looking at that. So do yourself and your trading account a favor.
Make it a good practice to have your local time synchronized with a time server. Either at every computer restart, manually or through some scheduled task.
There are several ways to go about this. You can hack your way around this and spend a full Sunday on this if you like. Or just take the simple route by getting a little tool. Make sure you consider a donation to the developer of this tool. It's well worth it.

Is trading a serious business or just your hobby?

My free e-book covers a few more risks to consider when you treat trading as a business an not a hobby. You can get the e-book by clicking here.
Questions? Let me know through the contact form on the main website.