I have seen legendary members say that they have a hard time finding posts to merit.
This is something I have read many times on the forum since the merit system was enabled, and I think it is not always easy to find a post worth rewarding with merit. Some Legendary members (who are also merit sources) have preferred parts of the forum they visit and their merit distribution is limited to those parts of the forum. There are a lot of good posts that are simply cluttered with a lot of spam and there are few who want to look for something worth meriting at all in a pile of garbage.
What happens is that if time passes until I get it, days for example, in the end I don't come back. I have decided that when I get a smerit, instead of meriting a previous post, I keep surfing the forum and give the merit to the next post I find worthy of merit.
I don't think you should bother so much with the fact that you don't have a sMerit at one point - listen to the advice of others and save it in bookmarks if you think it really deserves to be rewarded. I will tell you that it is never too late to go back in time and reward someone. I will give you an example of how I got the merit for my 2015 post years after I wrote it
https://bitcointalk.org/index.php?topic=1173044.msg12372803#msg12372803