The labels shown for `ucstart` and `ucend` parameters in the `list=usercontribs` API query are as shown below.
Note that `ucstart` is the later timestamp and `ucend` is the earlier one (for example https://en.wikipedia.org/w/api.php?action=query&format=json&list=usercontribs&ucstart=2020-09-14T00%3A00%3A00.000Z&ucend=2019-09-14T00%3A00%3A00.000Z&ucuser=Huji returns results but https://en.wikipedia.org/w/api.php?action=query&format=json&list=usercontribs&ucstart=2019-09-14T00%3A00%3A00.000Z&ucend=2020-09-14T00%3A00%3A00.000Z&ucuser=Huji does not). The current label uses teh word "start timestamp" and "end timestamp" which implies the opposite, unless you know MW well-enough to relize that contribs are shown from later to earlier.
I suggest we change the labels to clearly say "earlier time" and "later time".
{F32350754}