Enter standby manually on Macbook I have set my MacBook to forget the filevault password after going into standby (not sleep) after a few hours. This works great, but sometimes I don't want to wait that long for the system to go to standby. So is there a way I can force going into standby immediately?

I know the 'pmset sleepnow', so I was hoping there is something like 'pmset standbynow', but I cannot seem to find it.
Standby is effectively hibernate mode, one of the several versions of sleep. It's actually possible to set the sleep mode, then call pmset sleepnow.

Let's go over each of the sleep modes:

0 - Old style sleep mode, with RAM powered on while sleeping, safe sleep disabled, and super-fast wake.

1 - Hibernation mode, with RAM contents written to disk, system totally shut down while “sleeping,” and slower wake up, due to reading the contents of RAM off the hard drive. (Deprecated)

3 - The default mode on machines introduced since about fall 2005. RAM is powered on while sleeping, but RAM contents are also written to disk before sleeping. In the event of total power loss, the system enters hibernation mode automatically.

5 - This is the same as mode 1, but it’s for those using secure virtual memory (in System Preferences -> Security). (Deprecated)

7 - This is the same as mode 3, but it’s for those using secure virtual memory.

25 -  The
     system will store a copy of memory to persistent storage (the disk), and
     will remove power to memory. The system will restore from disk image.

You can get more in depth information from the man page. Please read it, it contains more in depth info.

You're probably after 25. It's quite easy to set your sleep mode.

Just in case, first note down the current sleep mode in case something isn't working later. pmset -g | grep hibernatemode will tell you. Note this down somewhere. You can then set the sleep mode using sudo pmset -a hibernatemode MODE, which in you case would be sudo pmset -a hibernatemode 25.

If you want something that will hibernate without keeping the sleepmode as 25, you can use DeepSleep to hibernate on demand.