You're still relying on the central limit theorem (i.e. a reasonable amount of data) : using t instead of z just corrects for the fact that you only have sample

You're still relying on the central limit theorem (i.e. a reasonable amount of data) : using t instead of z just corrects for the fact that you only have sample variances instead of population variances. However, I suppose it's not unreasonable to assume that the ratings are likely to have a bell shaped distribution (which could be checked), so the normal/t approximation is probably going to be OK.