Lennox G40UH takes a long time for the heat to come on
Your furnace tries to ignite five times. If it fails, it goes into lockout for 60 minutes. Once the lockout period is up, it tries five more times.

From your description, it sounds like it's failing the first set of ignitions. This could be a problem with the gas flow, a bad igniter, a misaligned igniter, a dirty or bad flame sensor, etc.

The best way to start diagnosing the problem, is to observe the ignition sequence.  Set the thermostat to heat, and turn the set point down so the thermostat calls for heat.  Then go to the furnace, and watch/listen to what's happening. The normal ignition sequence will be something like...


Inducer fan starts.
15 seconds later the hot surface igniter heats up.
After 20 seconds the gas valve opens.
The gas ignites, and the flame sensor "proves" the flame.
After a delay, the blower will start.
The furnace runs until the thermostat is satisfied. 


If step 4 fails, the furnace tries four more times to ignite. If it still fails, it goes into the 60 minute lockout.