timeToCurrentFormat() --- How to remove frames

there is also the "interfaces instead of code solution" of iExpressions:

https://mamoworld.com/after-effects-expression/counter-time

It allows very flexible and easy formatting of the counter and generates the expressions for you, so there is no need to read or write any code.

A classic:

http://www.motionscript.com/design-guide/up-down-clock.html

Mylenium

The timetoCurrentFormat() expression is going to do exactly what it says, convert time to your current format, which likely means that your comp's time display is in frames. 

If you hold Ctrl and click the blue frame counter in the top-left of your comp then it will switch to timecode and so will your text. Check out the attached screenshot for where you can change this. You can also change it in Project Settings > Time Display Style > Timecode

If you want something that's more reliable (especially if you'll be sharing this project and each user will have different settings) then you might want to consider using the Timecode effect under Effects & Presets > Text >Timecode.