I am in favor of enabling quotes in locked topics. But you can use
epochconverter for adding the time of quoted post.
Enter the exact time the post was created and click on "Human date to Timestamp" button. Then Epoch timestamp will be shown.
Yeah, there is some alternative methods to quote from locked topics, but I think that they require too much hassle. Simple solution would be really needed. Because we often need to quote from locked topics, especially when we are talking about historic topics. Personally when I need to do it, I just copy text, insert it into quote tag and add link to original post above or under quote. For me it's simpliest way to quote from locked topic.