I don't know about Lexapro, but klonopin should likely be taken at a regular basis through the day. It's a slow on/slow off drug that, that for some can take up to 4-8 hours to reach peak plasma concentrations. For some the effect of the drug is much sooner.

If it appears to not be working to control anxiety, then I would talk to the doc about dosing scheduling rather than upping the dose.