In the future, when you want help with a weakaura, you need to share it. The best way is to export the weakaura string to https://wago.io and then post the link here. Since you're a new account, you can drop the https:// part of the link so people can see it.
I'm going to assume you created a dynamic group that contains an auto cloning icon group to display your buffs. Put %c in the display box for the dynamic group and then put the following function in the custom function box that pops up:
Code:
function(exp)
return exp and exp>0 and format(SecondsToTimeAbbrev(exp-GetTime())) or ""
end
This will display text on the icon exactly how Blizzard's buff frame displays remaining time.