You can get the current time with
And you can format this with
strftime() by passing it as the second argument:
:echo strftime('%T', localtime())
And you can modify it as well:
:echo strftime('%T', localtime() + 60 * 25)
So for your command it'll be something like:
:put =strftime('%T', localtime() + 60 * 25)
In reality, you probably want to save the
localtime() and then insert
strftime('%T', time) and
strftime('%T', time + 60 * 25), because otherwise you might risk the time between the two operations being just long enough for it to be off by one second/minute. You can also round it to 25-minute intervals with some more math.
:help localtime() and
:help strftime() for more information on all of the above.
:help function-list is also very useful, which includes a "date and time" section. Also see How do I navigate to topics in Vim's documentation?