SQL hourly log , show all matching rows that have a value below threshold for n hours

I have a simple SQL log table (named market_history in SQLite) for US markets it looks something like this:

Sample table (market_history)

id  datetime        market    percent 
1   9/5/2014 7:50   ARIZONA      50.0 
2   9/5/2014 7:50   ATLANTA      97.4 
3   9/5/2014 7:50   AUSTIN       78.8 
4   9/5/2014 7:50   BOSTON       90.9 
6   9/5/2014 7:50   CHARLOTTE    100.0 
7   9/5/2014 7:50   CHICAGO      90.3 

This table is an hourly snapshot of network capacity in various systems in each market. What I would like to do is set up an alert system that if any one particular market is below a threshold percent (say 50) for more than 2 consecutive hours (each row is recorded every hour), it triggers an alert email.. So the query should show me a a unique list of Market names where the percents is < 50.0 for more than the last 2 consecutive entries

Here's the SQL I'm trying, but it's not working:

Sample SQL (not working):

SELECT 
mh.datetime, mh.market, mh.percent
 FROM  markets_history mh
WHERE
 (SELECT mh1.precent FROM markets_history mh1 WHERE  mh1.datetime BETWEEN "2015-03-23 00:00:00" AND "2015-03-23 00:59:59" AND mh.market=mh1.market ) < 50 AND (SELECT mh2.precent FROM markets_history mh2 WHERE  mh2.datetime BETWEEN "2015-03-23 01:00:00" AND "2015-03-23 01:59:59" AND mh.market=mh2.market ) < 50
ORDER by mh.datetime

I know I'm missing something.. any sugggestions