Here's a nice hacked up version, note the mkdir -p that makes the directory if it doesn't exist. Also I changed the time from 24hr to more provincial 12hr w/ AM/PM Please be careful adding aliases if you aren't sure what' they're doing!

alias journal='mkdir -p /Users/insert_your_username_here_on_mac_on_linux_change_Users_to_home_on_windows_good_luck/journal/$(date +%Y)/; vim + "/Users/insert_your_username_here_on_mac_on_linux_change_Users_to_home_on_windows_good_luck/journal/$(date +%Y)/$(date +%Y-%m-%d).md" -c "execute \"normal! Go$(date +%r)\<CR>========\<CR>\" | startinsert "'