The Precepts are optional vows. Laypeople are advised to follow the first 5 percepts, but unless you have vowed to follow them, even then you are not committed to doing so. You should try to follow them, but you do not need to take an actual vow in order to do so. As with all Buddhist vows, there are particular formats to be used.
The Precept on meals is one of the extra vows taken by monks and nuns.
This precept is also taken when a layperson does the sojong vow bimonthly ... which is again, optional. Here is a site that discusses it. Because my training is in Tibetan Buddhism, this is the only branch of Buddhism I can speak about.
http://www.kagyu-asia.com/t_significance_sojong.html
If you decide to undertake the sojong, the precept on eating only at the proper times allows you to drink water, juice, coffee or tea throughout the day. But it does include prohibitions against drinking milk (including in coffee or tea) or bouillon. Your two meals on the sojong day cannot have any animal products in them. Furthermore, you are allowed two meals on a sojong day (if you decide to participate in the sojong): one before sunrise, and one at noon.
