[Seerah]

It wouldn't be too bad, but using the event is much easier in addition to being lighter on resources.

local function HideUI()
     UIParent:Hide()
end
 
local f = CreateFrame("Frame")
f:RegisterEvent("PLAYER_STOPPED_MOVING")
f:RegisterEvent("PLAYER_STARTED_MOVING")
 
f:SetScript("OnEvent", function(self, event)
     if event == "PLAYER_STOPPED_MOVING" then
          C_Timer.After(3, HideUI)
     end
     if event == "PLAYER_STARTED_MOVING" then
          UIParent:Show()
     end
end)