it largely depends on your content but their are a few universals when you get started
If I were you I wouldnt worry about Timezones or appealing to different countries at this point as, while it will become important once you've grown a bit, for now I'd just stick to worrying about the times and audience from where your based.
Sundays are a bit of a gamble of a day, if you publish your videos super early in the morning you may do alright on a Sunday (again depending on your content) but generally people tend to be busy on sundays getting ready for the week ahead so views tend to be down on the whole across youtube once you get past midday.
Weekdays tend to do alright; Mondays and Fridays in particular as most people tend to come home from work or school on monday evenings and spend there evening online and friday evenings, especially now, its all about having a few beers (or glasses of wine) and enjoying whatevers on youtube, twitch or netflix rather than going out. but I should also say that a lot of people tend to publish on mondays and fridays so depedning on your content you may have some fierce competition. so maybe look at a midweek roll out till you've grown a bit (Tuesdays, Wednesdays or Thursdays) they tend to be quieter days on the publishing front so you'd probably clean up quite nicely on there
It'll be a while before you get solid and reliable analyitics (Im only just breaking 400 subs and 80k views and my analytics are only NOW starting to give me any kind of meaningful information) but generally once you pick a day and time, stick with it for a while and let the familiarity build up with your audience
that way you'll keep them coming back or checking your channel around that time to see if you've put anything new up.
(For reference I make film reviews and I've been publishing every Friday at 2:30pm now for a couple of years. when I finally unlocked "Best time to post" data on my analytics it told me to basically stay where I was but upload and hour or two earlier which im considering doing in the new year)