When your memes barely reach 5 upvotes

Hard to tell, I have yet to learn it myself

Generally in the morning, a bit before the "rush hour" traffic. People will generally go through posts before they post any themselves, so you'll have the best chance of getting enough up votes to boost it to the front page before it gets lost in the sea of lesser memes.

So, either early morning or late evening - do NOT post late afternoon to early evening until you have the reputation of Laughing Fish and can ignore such rules.