No idea if this is was the commenter was implying, but I think the advice is because plenty of apps can send requests in the 1 second initial window as you auth

No idea if this is was the commenter was implying, but I think the advice is because plenty of apps can send requests in the 1 second initial window as you authenticate your VPN. In theory, that could be sensitive data or enable a sophisticated attacker to correlate you with your VPN exit (if you were using it for pseudo-anonymity). I don't think key negotiation is compromised in any way...