The etiquette on Steemit is very much defined, and enforced, by the users with the largest investments in the platform. They have the most to lose if Steemit fails, and the most to gain if it does well. Only very recently, the account @grumpycat started to flag posts older than 3.5 days that bought upvotes after this time.
But I've just put $0.5 SBD into minnowbooster on a post that's 4 days old.
I would not worry. The upvote buying that is being countered is on the order of hundreds of SBD, and flags are only used to return huge paid upvotes to zero. You should not even crop up on the radar.
The best time to buy upvotes is soon after posting. This way, the extra vote weight helps your post get onto the Hot and Trending feeds which gives you exposure. After a post is several days old, even a massive upvote is unlikely to return it to those feeds.
Ah I see, thanks for the clarification and reassurance. I suppose when you look at it that way, I can see why "whales" would want to make sure everything is running steadily and efficiently without corruption.
Oh and thank you for the large up vote too!
By the way, I'm curious, do you enjoy your Biomedical Programming job? It sounds very interesting, I studied Biomedical Science myself and did a year in Computing afterwards so it fits my educational background quite well.