I would request clarification from provider - 95 centile is usually over the course of the month, so you may be able to extend either the length of time before squashing or increase the bandwidth to take into account overnight periods, or vary the lengths depending on bursts. If if it 95th centile per 5 min period, then they're onto a winner as they're pretty much putting you on a constrained data amount (like being stuck with 20Mb on a 100Mb bearer) - most firms will charge you extra per Mb over CDR based on 95th centile based on 5 min average readings (which may be what the excess is, which is a much nicer amount than paying £8 for 37.5MB data), so for example, over a month, if I used 21Mb 95th centile rather than 20Mb, I'd pay an excess (which from a brief look at a transit provider, some pricing was £9 per Mb on 10Mb CDR - but that's probably an out of date page).

CDR vs 95th %tile - overselling? - that provides a bit of an overview of CDR/95th Centile and how it's all worked out.