Mikveh time should be just before dawn. It’s about 2.5 hours before sunrise. You can find the time of sunrise on most smartphones, usually in the weather app. If sunrise is 5:30am then best mikveh time is about 3:00 am. If the mikveh you will use have many in line then you can go earlier but not before the middle of the night. (Check my Zmanim.com or calculate the time between previous sunset and sunrise. (In Jerusalem it’s 12:38am and best mikveh time is 3:45am or earlier. In New York the best mikveh time is 3:15 am or earlier. Midnight is 12:54 am)

The first four is from the Holy Ari (see text image from the writings of the Ari.).
The fifth dip and meditation are from the Ben Ish Chai. It’s the YHVH with the nikud of Kamatz that is related to Keter. It connects us to the Supernal Keter and put a Crown on top of Zeir Anpin.  It gives us a renewed soul. Before the Mikveh it’s good to say (From Ben Ish Chai and suggested by Rabbi Ben Zion Mutzafi, Shlita), these three verses from Micha 7:15-18 and ask to receive holy soul for yourself, for your children and grandchildren.

מִי אֵל כָּמוֹךָ נֹשֵׂא עָו‍ֹן וְעֹבֵר עַל פֶּשַׁע לִשְׁאֵרִית נַחֲלָתוֹ לֹא הֶחֱזִיק לָעַד אַפּוֹ כִּי חָפֵץ חֶסֶד הוּא.
יָשׁוּב יְרַחֲמֵנוּ יִכְבֹּשׁ עֲו‍ֹנֹתֵינוּ וְתַשְׁלִיךְ בִּמְצֻלוֹת יָם כָּל חַטֹּאותָם.
תִּתֵּן אֱמֶת לְיַעֲקֹב חֶסֶד לְאַבְרָהָם אֲשֶׁר נִשְׁבַּעְתָּ לַאֲבֹתֵינוּ מִימֵי קֶדֶם. 

Since this special Mikveh is about soul connection and not spiritual cleansing, it’s important to dip in a mikveh (or any large body of water like sea, lake, river, or pool). A standard bath is not big enough for complete body immersion under water.
The complete process of receiving the extra soul is when we recite Shema Israel, during the Kedusha of the Musaf prayer.
Those who are not close to a mikveh and for some reason do the Shavuot connection at home, they can take a long shower and meditate to connect to the supernal Mikveh. It’s not the same but better than doing nothing.
If you have a ‘desert’ around you, meaning far from places to make this connect, just do your best and the study of this wisdom would elevate you as much as you desire (create a vessel for it). Always do your best. The Holy One Blessed be He, knows your heart and will reward you with light acording to your heart and efforts.
If you print the above meditation, treat it as sacred names and do not dispose of it unless you do it with other sacred text as properly required.
More on the night of Shavuot here:
Chag Shavuot Sameach