10pm my be pushing it if your flight is at all delayed. Look at flightstats.com or fr24.com for punctuality. Immigration is unpredictable but your bags will be checked through so no need to to wait for them. Pack what you need in your carry-ons.
Saturday night traffic is busy so I'd allow 30 mins to get from the airport area to downtown in a taxi. Make sure you know where the entrance is; Dubai Mall is massive and it's a brisk 15 min walk from the main mall entrance to the Burj entrance.
11pm should be doable.