Within reason, this can be as long or as short as you would like and will not effect the oveall number of impressions delivered. The difference is the concentration of delivery (i.e a short timeframe will mean your advert will experience a comparatively high concentration of impressions, compared to a longer campaign, which will experience more steady impressions).
That said, we reccomend allowing a minimum of 7 days per 150,000 impressions purchased on an asset. If you are wanting to book a longer term campaign, please email advertising@edfringe.com and the team can help.
Please select the type(s) of advert you want to book and then select the number of thousand impressions you would like for each.