Yes when FedEx tracking says on FedEx vehicle for delivery it means that you will get the package that day.
So if your package is coming through FedEx and the tracking says On FedEx vehicle for delivery today then you should get the package today.
FedEx delivers as early as 8:00 AM to as late as 8:00 PM in some places and so you should get your package between those hours.
There's no specific time that FedEx delivers to houses during the day and so you could get the package in the afternoon hours or later.
I get my FedEx packages around 2:40 PM here but the time can vary.
If the FedEx package does not require a signature then the FedEx driver will just leave the package someplace on your porch or somewhere around your front door.