This work will take at most one hour.
彼の英語はせいぜい中学レベルだ。
His English is at best junior high school level.
as much as possible; to the utmost
Used when encouraging someone to do their best within their limits, or when stating one will do all one can. Often appears in expressions like せいぜい頑張る.
明日の試験、せいぜい頑張ってね。
Do your best on tomorrow's exam.
私もせいぜい努力します。
I'll do my utmost as well.
The bonus for this job is at most about 50,000 yen.
I don't have much talent, but I intend to do my best anyway.
There's at most two days' worth of food in the fridge.
If you're so confident, go ahead and do your best (we'll see).