These engineers will be sent to the SLS as it sits right there on the pad, in an effort to “gather as much data as possible to understand the cause of the issue” while the hardware is under cryogenic conditions, something the VAB cannot offer. To allow these people to work there, and protect the rocket from the elements, an enclosure will be erected around the site.
It’s not clear yet how long replacing the seal will take, but NASA says it may return the rocket to the VAB for additional work. In fact, it kind of has to, as requirements for the certification on the flight termination system require the batteries to be reset, and the VAB is where that should be done.
As for the next launch date, there’s nothing certain about it yet. NASA will probably miss the current launch window period, which ends on October 4, but if it moves fast enough, it might get the thing flying between October 17 and October 31, when eleven launch opportunities line up.
November and December too come with launch opportunities, so we’re still in the cards to see Artemis I depart by the end of this year.