AM vs PM
When I add a new task for "tod at 4" and it's 11am, the service should be smart enough to realize that I mean "today at 4pm" rather than "today at 4am"
In general, it should not even use AM as the default for 12-6 hour timeframe. In 99% of the cases, I mean 4pm, not 4am.
If your default time settings are the 12-hour time settings then unfortunately you must specify if the time should be am or pm, but you can choose to use the 24-hour settings and then add a task due "tod at 16" instead.
To change your time settings, log into the web-app, go to the Settings (gear icon in top-right corner) and choose your preferred time format on the "General" tab.