If you have a Blockland key (not just a steam gift key), which would be a copy of Blockland that was purchased outside of Steam, then yes. You can just open that multiple times.
But there is a solution to Steam.
1) Go into the Steam Blockland folder, where blockland.exe is.
2) Create a new text file in here (Right click in the folder > new > Text Document) and name it steam_appid
3) Open the file and paste this into it and save:
250340
4) Make a new shortcut for blockland.exe, probably on the desktop if most convenient.
5) Right click that shortcut and select Properties
6) At the very end of the "Target:" field, add this (don't delete any existing text):
ptlaaxobimwroe -steam
(it should now look something like...)
"C:\Program Files(x86)\steam\steamapps\common\Blockland\blockland.exe" ptlaaxobimwroe -steam"
7) You should now be able to open it as many times as you want through this shortcut, and you'll still have the overlay, achievements, and hours logged.