Antonym of Overlap?

Solution 1:

The word 'margin' has this exact meaning.

Margin - noun

2. an amount allowed or available beyond what is actually necessary: to allow a margin for error.

www.dictionary.com

e.g. "...between 22:45 and 00:15 UTC (i.e. 15 minutes margin either side of the window)"

Solution 2:

gap?

(i.e. additional 15 minutes on either side of the window to ensure the gap)"

or in this case, would margin of safety work for you?

Solution 3:

You're creating a metaphorical...

buffer zone - any area serving to mitigate or neutralize potential conflict. _{^{(thefreedictionary)}}

Solution 4:

It's not exactly an antonym but what you want is separation to avoid interference.

2 The division of something into constituent or distinct elements:
'prose structured into short sentences with meaningful separation into paragraphs'

Reference:
http://www.oxforddictionaries.com/definition/english/separation