I don't develop in trays anymore, but I used to use a metronome. Counting seconds is your best friend...

It gets to become a habit and second nature after a while. Some people can't stand it.
If you have trays anyway, learn how to develop by inspection with a dark green safelight. Time development can, and is in many ways, very precise. But as an extra safety measure I used it to turn on the lights for a brief moment at about 75% of my normal dev time. Have a look, then either dunk the film into the stop bath or let it continue developing as needed. It's pretty slick, if you can avoid all other problems such as scratches and uneven development.
Re: Metronome. It's a brilliant tool for me since I print in silver. This way I can get very precise dodging and burning done by just letting the enlarger lamp continue to illuminate while I do my thing with various tools, so if you print in silver it could be worth it for that reason too. Then if you decide you don't like it for film developing, well, you can still use the metronome.
- Thomas