Sunrise in Surabaya was about 5:14 local time. The sun was up the whole flight as far as I can tell.
Just checked again - you are correct. Was dawn in the area of last known position at the time of departure, but was daylight an hour later at time plane disappeared.
There have been wreckage found only after extensive searching at the same exact area for months.
You can't have it both ways however. Most scenarios which cause sudden loss of communications will cause lots of debris. Conversely, most scenarios that cause minimal debris imply control and hence communications should be maintained.
Sudden loss of all communications could be due to catastrophic structural failure which would cause lots of debris, or an AF447 like event which also caused fragmentation at impact and lots of floating debris. They found lots of debris fairly quickly (days) with AF447 - even though
i. the initial search was delayed by at least a day
ii. the search area was much larger (they didn't "see" loss of the transponder with 447)
iii. the search area was mid-ocean (severely complicating the search by limiting aircraft time on scene and delaying arrival of ships).
None of that applies here.
There simply are not that many explanations for sudden loss of all communications and no debris - especially in a small area.
First Adm Sigit Setiayana, commander of Indonesia's Naval Aviation Center at Surabaya air force base, says 12 navy ships, five planes, three helicopters and a number of warships are taking part in the search, along with ships and planes from Singapore and Malaysia, the Associated Press reports.
Singapore, Malaysia, and Australian assets also looking.
If nothing is found today, we will need to contemplate other explanations.