I don't think I'd ever do an embargo in a cold pitch. My experience is that cooperation is best assured with an incentive structure, and you don't really have the power in a cold email to assure any kind of incentive structure. Unless there's a compelling follow-up story or they fear the wrath of somebody you are associated with, the reporter has zero reason to care what you think or ask for. Being too aggressive in demanding an embargo can come across as an idle threat, which is somewhere between a turn-off and dangerous.

My solution to this is to pitch stories that don't require embargos. "We exist, and we are great" is generally not a tactic I have had much success with anyway. Your affiliations and successes serve as credibility the week of your funding/launch just as well as they do on the day of your funding/launch. The only thing you're gambling on is the time-sensitivity.

I solve this by focusing on the angle. If you tie yourself into an existing popular media narrative/topic/event with a short lifespan, they have to cover you promptly. You also increase your chances of being covered because now you're offering an educated hot take on something everybody is already scrambling to cover. This also boosts social engagement, if you're going for that.