In fact, you don't want everyone to go in at the same time. The tanks need to go in first because their challenge is on a strict timer (usually longer than the DPS) and they need to be the first ones to complete the challenge. Since you can no longer cheese the tank challenge by keeping one tank outside to deal with Raptus, you need to get your tanks back in the fray before anyone else, otherwise Raptus will one-shot the DPS who was challenged.
We generally do tanks (right away) > healers (delay 3-5 seconds) > dps (delay another 5-7 seconds). Our DPS finish their challenge in about 14-15 seconds, so that means they'll generally be finishing up right around the time that the tanks get solidly out of their portal and are in range to taunt Raptus.
You can still one tank the challenge, our powertech tank still does it solo. Not sure about other tanks.
Regardless, the waiting tip is pretty good for ops teams that cannot the tank challenge solo