All Praise to Allah Subhanahu wa Taala and blessings of Him be on Prophet Muhammad peace be upon him His family and companions.
Rasulullah peace be upon him has asked to mention the name of Allah Swt before eating so its not specifically for the whole meal anything one eats or drink, entering into washroom, intercourse, before sleeping, leaving home, travel, and after waking up, closing doors, covering pots, etc. So any good time you could mention Bismillah (In the name of Allah) as by saying bismillah blessings are acheived. When we start our salah so in dua isteftah we recite "Tabarakasmuka" means your name is "blessed".
Below are some ahadith regarding saying Bismillah before different acts which shows its significance:
'Aishah (May Allah be pleased with her) reported: Messenger of Allah
(ﷺ) said, "When any of you wants to eat, he should mention the Name of
Allah in the begining, (i.e., say Bismillah). If he forgets to do it
in the beginning, he should say Bismillah awwalahu wa akhirahu (I
begin with the Name of Allah at the beginning and at the end)."
[At-Tirmidhi and Abu Dawud].
Jabir reported the Prophet (ﷺ) as saying: Shut your door and make
mention of Allah's name, for the devil does not open a door which has
been shut; extinguish your lamp and make mention of Allah's name,
cover up your vessel even by a piece of wood that you just put on it
and make mention of Allah's name, and tie up your water-skin
mentioning Allah's name.(Abi dawud)
Narrated Ibn `Abbas: The Prophet (ﷺ) said, "If anyone of you, when
having sexual intercourse with his wife, says: Bismillah, Allahumma
jannibni-Sh-Shaitan wa jannib-ish-Shaitan ma razaqtana, and if it is
destined that they should have a child, then Satan will never be able
to harm him."(Bukhari)
Abu Ayyub Ansaari Radiyallahu'Anhu reports: "We were once present in
the assembly of Rasulullah Sallallahu 'Alayhi Wasallam. Food was
brought to him. 1 did not observe any food that had so much barakah at
the beginning and at the end of which there was no barakah left in the
food. We therefore asked Rasulullah Sallallahu 'Alayhi Wasallam
reason?. He replied: 'In the beginning we all recited 'Bismillah'
before we began eating. Then someone in the end joined us, and did not
recite ''Bismillah'. The shaitaan ate with him'".(Shamail
Ibn 'Abbas (May Allah be pleased with them) reported: Messenger of
Allah (ﷺ) said, "Do not drink in one gulp like a camel, but in two or
three (gulps). Mention the Name of Allah (i.e., say Bismillah) when
you start drinking and praise Him (i.e., say Al-hamdu lillah) after
you have finished (drinking)." [At- Tirmidhi].
Allah Swt and His Messenger know best.