I think the exact minutes elapsed from WT being last seen to him being noticed missing has not been stated by LE, but whether it is 10 minutes or 1 minute, it is a very short time, which should make the case easier to solve. Compare with the C Lawrence case where the elapsed time is many hours, which makes it harder to solve.
yes, i agree, so much easier to pinpoint peoples said and actual whereabouts in that 15mins timeframe, especially with phone pings and possible cctv footage etc
im sure they know and watching someone, just need that other person who supplied the alibi to step up