Stress mark of утро

Question

The stress of the word утро seems to be irregular, since it depends on the absence or presence of a preposition.

According to some sources:

1. the stress is always у́тр- without a preposition.
2. the stress is always утр-́ after a preposition.

However, it's again утр-́ not necessarily after a preposition. Examples:

3. A dictionary of mine cites "в семь часов утра́"
4. Some books cite утро́м (or at least рано утро́м) to mean "in the morning".

So, what is the correct stress in each context?

Answer 1

1. Almost true. Without a preposition stress is almost always on the first syllable

рано ýтром
каждое ýтро

Except the word утра́ with preposition к, в, до etc in the following phrases:

[preposition] [time] утра́

к 8 часам утра́
в 7 часов утра́
до 6 часов утра́

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2. Wrong. Not always.
   Examples:

для [раннего] ýтра
в [столь раннее] ýтро

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3. Correct. See the 1st item.

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4. Wrong. The correct stress is on the first syllable:

рано ýтром

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Bonus pack.
There are also adverbs constructed from preposition and the word утро. They should be memorized.

поутрý
наýтро

Answer 2

1.the stress is always у́тр- without a preposition.--Correct. .

2.the stress is always утр-́ after a preposition.--No, not always.

об у'тре, для такого у'тра, в это у'тро.

3.A dictionary of mine cites "в семь часов утра́"--Correct, an expression, should be memorized.

4 Some books cite утро́м (or at least рано утро́м) to mean "in the morning"No, this isn't correct. It should be "у'тром",the same "рано у'тром."