This has been well documented on the web with many tutorials. It will take as long as it takes to install windows and ubuntu. Which will be about 3 hours. If you want to recover that data on your previous install, that is a different problem.
You might already have the option to boot into windows. Check if these instructions on how Grub the application that loads the different operating system works. It may help you to just display the option to load the system you want windows or Ubuntu at start up.
https://help.ubuntu.com/community/Grub2#Boot Display Behavior
official Ubuntu documentation.
Here is a video going through the steps
If you want to install windows after Ubuntu. You will need to reinstall grub. Windows automatically over writes the MBR, portion of you hard drives partitions and breaks your ability to boot into Ubuntu. These instructions will explain how to fix your boot loader by reinstalling grub.
https://help.ubuntu.com/community/Grub2#Reinstalling GRUB 2
You will still need to create space for your windows installation. Assuming that you install Ubuntu on to your disk with one partition covering the whole disk.If you need to shrink a partition, you need to boot up on a live disk and open gparted. It gives you the option to resize a partition but you can not do this on a mounted or disk. Which is why you need to boot up into a live disk. Here are screen shot of how to do that.
I recommend understanding how partitioning works specifically the MBR or master boot record. You need to understand the limitations such as you can only have 4 primary partitions. An extended partition need to occupy the entire remaining disk space if you want to have more then 4 primary partitions.