Hardyness zones are an indication for the average lowest temperature in a specific area.
Almost all bulbs do well in US zones, but some bulbs need special treatment in extreme heat or cold area's.

Take your zone into account when buying bulbs but be aware that your zone is an indication and that specific situations in your garden can create micro climates that deviate from the hardyness indicated.

day lilies ?? Yes, as each flower lasts only a single day. But do not worry, new flower buds will appear daily during the summer.