Something that's optimal is the best or most favorable for a given situation. Flowers? Check. Chocolates? Check. Dinner reservation? Check. Sounds like you have the optimal conditions for a successful anniversary date.
There's an implication with optimal that certain restrictions exist in a given situation, so that what is optimal isn't necessarily the ideal scenario — it's the best one given those limitations. For example, optimal population levels for a species are not the highest levels — instead they're the best levels that a particular environment can sustain. Often the word optimum is used interchangeably with optimal.