a day or two,one or two days 后面的动词分别用单数还是复数?

问题描述:

a day or two,one or two days 后面的动词分别用单数还是复数?

因为都表示一段时间,它们做主语的时候谓语都要用单数.
比如:one or two days is not enough for this mission.