It is common practice when hiring a developer to pay them for time spent programming if it's any significant amount. I've never heard of paying for all the time

It is common practice when hiring a developer to pay them for time spent programming if it's any significant amount. I've never heard of paying for all the time spent in the interview, or for time spent if it's just something small and simple to get a quick feel for skill. But if they're asking for more than an hour or two or if they're asking for new features added to their existing code base, it's completely fair to ask for compensation.