@jph – thanks for sharing your point of view.
Based on your input I’m going to suggest to Wave that they start supporting the ISO 8601 standard (combined date and time representations). Hopefully doing that can lead to a solution 
I must say though that I’m not sure that agree with you on this. Well, I do understand that you prefer the ISO standard and why it’s generally good to stick to standards. However, in this case, there are clearly a lot of people that are struggling with this chosen date format as a lot of other software doesn’t seem to play well with it for whatever reason (ie. Excel, Numbers, Google Sheets, Wave and more). So although it’s good to stick to a standard, I wonder if it’s counterproductive in this case and if the standard is the right one…? (for example; a unix timestamp is another very common and very compatible standard/format).
Alternatively, I wonder if Monzo would consider both including the current ISO standard date format as well as one of the many suggested date formats that Wave have put forward [see list above] – just to make life easier for the many non-techy Monzo users
Hope you can see where I am coming from, and again, thanks for sharing your point of view!