A few months I made a
dashboard with block data . If you click the button "Last Week", you will see that there were 3 empty blocks mined last week:
block id pool blocktime
691877 AntPool 00:01:15
692142 AntPool 00:15:49
692222 ViaBTC 00:07:40
Except for the first one, the other two had a normal blocktime. And 1 minute is more than enough to add transactions from the mempool into a block.
UpdateTip at my node shows something different:
block pool blocktime realtime
691877 AntPool 00:01:15 00:00:15
692142 AntPool 00:15:49 00:00:01
692222 ViaBTC 00:07:40 00:00:10
So, we see only few seconds difference.