Baltic Capitals and Poland, Seeking Itinerary Advice

I'm afraid you're being way too optimistic about how much time you'll have at each destination. You arrive in Helsinki late on July 4, so that day doesn't count. (Even July 5 is somewhat questionable due to potential jetlag.) July 17 doesn't count since you'll be heading out to the airport really early. The usable days you'll have for the Baltic/Polish part of your trip are July 5 through July 16, a total of 12 days, on 5 of which you are changing base cities, most of which changes will take about half a day.

Yet if you total up the number if days you've listed for the various cities, it looks like you're expecting 17 day of sightseeing time. There is a massive difference between having 17 days to visit 6 major cities and having less than 12 days to visit those cities.

This is the way I'd figure your approximate available time (though for my own trips, I don't count travel days at all):

Helsinki: a bit less than 1 day
Tallinn: 1 day (if morning bus to Riga)
Riga: 1-1/2 days (if morning bus to Vilnius)
Vilnius: less than 2 days
Krakow: 2 days (if morning train to Warsaw)
Warsaw: 2-1/2 days

I don't think 12 days (before discounting travel time) is long enough for six such interesting cities. You haven't got too much time anywhere as far as I'm concerned, so I don't have any suggested reallocations unless you're actually planning a sightseeing visit to Podgorica (in which case, definitely skip it and use the time in one or two of the other cities).

Way too frenetic and not enough time in each city.

What are your interests? Why have you chosen those cities? What do you plan to do in each city?

FWIW I recently spent nine days in Riga, Gdansk and Warsaw. My itninerary was this:

Day 1: Fly Heathrow to Riga landing in Riga late afternoon.
Day 2: Riga
Day 3: Riga
Day 4: Mid morning flight to Gdansk
Day 5: Gdansk
Day 6: Gdansk (including day trip to Malbork Castle)
Day 7: Gdansk
Day 8: Morning train to Warsaw
Day 9: Flight from Warsaw to Heathrow

I've previously been to Warsaw on three separate occasions so my visit was primarily to catch up on a couple of things I wanted to do there and also because British Airways doesn't fly to Gdansk.

I've been to Tallinn previously, spent a long weekend there and felt that was sufficient.

I would like to have incorporated Vilnius but it would have meant shortchanging one of the other cities which I didn't want to do so that will have to wait for another time.

I was in all of those places last month, similar modes of transportation between cities, but in this order:

Krakow--4 nights

Warsaw--4 nights

Vilnius--3 nights

Riga--3 nights

Tallinn--3 nights

Helsinki--4 nights

The problem with you schedule is you are only giving yourself one day in most places. That's not a lot of time.

Your list of cities, days and nights are completely off.