Please tell me, will the baby be 5 months old on June 9th? We're being…

Please tell me, will the baby be 5 months old on June 9th? We're being invited to an event from 4 pm to 11 pm. If I pump and leave some for grandma, is it realistic? (The baby only breastfeeds). Maybe someone had similar situations with their little one ? It will be difficult for the baby to go out, he doesn't sleep in a stroller, only in a crib.