An option without the vesting period and the price at which one can exercise the option is of not much value.
If vesting is determined by board, then at any given point in time they can change the vesting period to say 3, 5, 10 years any number.
The other aspect is at what price you are allowed to exercise the option, ie if the stock is of value 10, you may be given an option to buy this at 10, 20 or 100. This has to be stated upfront for you to know the real value. On listing if the value is say 80, then if you have the option to exercise at 10, or 20 you would make money, else at 100 you loose money and hence choose not to exercise the option. However your having stuck around the company for "x" years in anticipation of making money would go waste.
Without a vesting period or the price to exercise the option, they are pretty much meaningless and would depend on the goodwill of the founders