I hear a lot of talk about how etfs affect the market. If an etf trades as a stock then I would think that it would be rare that they sell the underlying securities in their basket because they do not need to redeem or issue new shares like a mutual fund. Is the effect mostly that etfs tie up a lot of shares and therefore reduce the supply in the overall market? I hear market pundits say to buy more in the afternoon than in the morning due to redemptions but wouldn’t that only apply to mutual funds?

i know there are other concerns about liquidity but I try to buy etfs with higher trading volume and with bigger ownership.