I haven't done this in my reporting before, but I just tested out an example. If you go into the segment builder, even though the metric for time spent on site isn't there, you should see the dimension version of it. You can create a visit level segment using the "exclude" option, and then place the dimension in there for the values you want to remove. I used 40 seconds as an example because of the data in my dataset, but you can set it to 10 seconds, or any amount you need. Just bring in 'time spent per visit - granular', select "less than or equal to", put the upper limit of your range. Then set it to visit level and select 'exclude'.
The result will be all of the visits that were on your site for 11 seconds or longer. You can then use that segment in a calculated metric.
