That does sound like a lot of time, especially for something you can do yourself pretty quickly with a Nolo book. Did you get an estimate from him before you did this? And did he explain what he spent all that time on?
Lawyers and accountants are like auto repair shops - if you don't already have a good one you trust, it's always a good idea to get recommendations, ask for estimates, and shop around a bit. They're also like contract programmers: the ones who really know what they're doing may be more expensive per hour, but cheaper in the long haul because they can get the job done a lot quicker.
$1600 is certainly at the high end of what you'd want to pay for a federal trademark application but four hours isn't too unlikely if the law firm conducted a trademark clearance search. Also, did their legal fees cover the $325 USPTO filing fee? I work with startups regularly and assist with trademark applications at a flat fee but I'd say 1-3 hours per application is the norm. Each application (and client) is different. Online services like Nolo can be convenient for helping complete the application form but there's a wide range of related counseling that these services don't provide (e.g. registration includes the responsibility to prevent others from using confusingly similar marks, meaning you should expect to incur related enforcement costs in the future or risk losing the trademark). Find a good attorney and start building a strong lasting relationship. Your IP assets will be some of the most valuable your business owns so protect them as best you can.