That was the case earlier in the Comp’s history – everyone used to post their giant review threads all at once in the newsgroups as soon as the Comp ended – but for the past I think 5-10 years, that rule’s been changed, so now you typically see lots of reviews cropping up during the Comp.
There are two informal norms that I don’t think are actual rules, but are good practices to my mind: 1) many reviewers don’t assign numerical ratings and/or put their reviews on IFDB until after the Comp is ended; this can help reduce the risk of biasing judges before they play a game; and 2) authors generally keep their reviews of other games to the authors-only forum, so they’re not publicly commenting on competitors’ work during the Comp (since authors can now be general judges, I suppose this technically doesn’t matter as much, but I think it’s still nice and collegial).
You could see it that way, which is I think an extra incentive to aim for thoughtful, even-handed evaluation when reviewing.