Generally, it is safe to leave your basking light on all day. But this is dependent on the foreseeable weather conditions that you face in your area. If you know that your room might get too hot, i.e. the weather in your area is expected to get warmer than usual, and you have no climate control such as an AC to cool down the room, you might want to have a plan to turn off that basking bulb if the basking area gets too hot.
Usually, the basking light can be left on during the normal 12-hour day/night cycle. Lots of people leave their basking lights on all day. And others, like myself, put the light on a timer to turn on/off multiple times a day for shorter intervals. A basking interval of 30 minutes multiple times throughout the day is a decent length that you can shoot for. I usually leave the basking light on constantly until the ambient temperature gets close to the acceptable range, then I will turn it off and on throughout the day.
In your situation, yes, leaving the basking light on for one day until you get back from work is alright. If this is a longer light schedule than usual for your chameleon, don't be surprised to see him sleeping with the lights on when you get back from work.
I should also note that not turning on the basking light for one day should also not pose an issue for a chameleon (assuming that the ambient temps are in the acceptable range). Heat kills reptiles far faster than the cold. If you are unsure about how hot the basking temperature will get, then it might be better to leave the light off. However, if you are confident that the basking temp won't get too hot, then leaving it on all day is perfectly fine.
