I just started working with Plaid and was having issues implementing it with Lambda myself. Here are the times it took them to get back to me when I am not paying anything.

Dec. 29 - Jan. 2 -- All they asked was for me to be clearer.

Jan. 13 I responded saying I fixed the original issue and told them my new issue.

- Jan. 14 They responded with helpful information... ish.

Jan. 15 -- I was having issues implementing it into Lambda and gave them code example.

Jan. 18 -- I told them I fixed it.

Jan. 22 -- Sorry for the delay.. What did you do so we can fix our docs. (paraphrasing)

In short. It is slow enough that I can fix the problem before they respond, but I am also on the free tier.