Coding to say Just Called Person at [city] 21 minutes ago

I would some js or php linked coding (for a html page) to show text that says 'Just called Person at [city] 21 minutes' ago where: 1. The city is selected randomly from a list of say 300 city names I will provide. 2. The 21 minutes changes. The range will vary between 1 minute and up to 3 hours (I would like to be able to vary the 3 hours to whatever I want). The minutes will change so 1 minute ago, 2 minutes ago etc until we have a new matter so starts back at 1 minutes etc. New matters only to be started during normal business hours/days. So for example at 10pm it would say at least 5 hours ago - assuming a 5pm normal business hours. Also only business days - but variable). Finally, if we access site with 1 browser and it says 21 minutes ago etc and then refresh or access site using another browser it must be the same, so cannot just be totally random. Thanks