how are third party bridges like orbiter finance able reduce the withdrawal time from base to eth from 7 days to almost instantaneous? and how does that affect the challenge period built into op stack?

/humpty | noun 558 | content creator, startup advisor, helping awesome people build cool sh*t /cryptosapiens /earlymorningcrew

They run both the source and sink chains and thus have high level of  guarantee that there are no invalid state transitions. They are mostly charging for the time value of money.