If you flight is in time and sit in front of the plane, you will arrive at or around B35 at 9.55, have cleared immigration at 10.00 and have collected you luggage from carousel 14 or so at 10.15, take the elevator up and arrive at the SQ desk at 10.20. If you plane is not in time, add the relevant delay to this schedule. Having said this, I do take the early morning flight from LHR quite frequently and it appears to be notoriously on time. Regarding security: They now show the waiting times for each pier. If security at A is slow, you can go through B, too, and walk airside to A. This does not make a big difference, it is all in the range of a few minutes. Düsseldorf is one of the easiest bigger airports in Germany to navigate. You could consider the LCY flight, which is scheduled to arrive 10 minutes earlier, but to my recollection the plane for this flight already comes from DUS in the morning....