Making Kiddush as soon as one arrives home:
It is a Mitzvah Min Hamuvchar to recite Kiddush as close to the entrance of Shabbos as possible. [This especially applies if one has hungry guests or family members waiting to start the meal. It goes without saying that one should not sit and talk with friends and delay the making of Kiddush.] Nevertheless, the central fulfillment of the Mitzvah continues to apply throughout the night [and thus, if one did not make Kiddush close to the entrance of Shabbos he is to do so any time at night].
Arrived from Shul before night: Even if one arrived [home] from Shul prior to night, he is to recite Kiddush immediately [upon returning home] even though it is still daytime. He is likewise required to eat the meal immediately after Kiddush in order so the Kiddush be Bemakom Seuda. [If, however, it is within a half hour to Tzeis Hakochavim, he is not to wash on bread until after he reads Kerias Shema after Tzeis Hakochavim. He may however make Kiddush and eat a Kezayis of Mezonos within this half hour.]
If one is not hungry: If one is not hungry and thus does not desire to eat as soon as he arrives home from Shul, he may delay making Kiddush [and eating the meal] until whatever time of night he desires, in order so he can eat with an appetite. [Nevertheless, if one has hungry guests or family members, he is not to delay starting the meal even if he is not currently hungry.]
Not to make Kiddush between 6:00 and 7:00: See next Halacha!
One is to recite Kiddush and eat the meal as soon as he arrives home from Shul, even if it is before nightfall, unless one is not hungry in which case he may delay the meal.
Justifiable reasons to delay Kiddush:
If there are valid reasons to delay Kiddush from being made right away then one may do so. Thus, one may Daven Bearichus, or participate in a Shiur Torah prior to Kiddush, or wait for guests to arrive, or be particular against making Kiddush between 6:00-7:00, even though this causes Kiddush to be delayed.
Not to delay Kiddush if people are hungry:
Even in the event of justifiable reasons to delay starting the meal, one is not to delay the meal if one has hungry guests or family members that are waiting on him. The Chofetz Chaim would not even sing the hymn of Shalom Aleichem when he had guests in order to start the meal right away.
What to do in the interim if one will not be making Kiddush right away:
If one does not plan to start the meal immediately upon arriving home from Shul, he is nevertheless to say Good Shabbos, and sing Shalom Aleichem and Eishes Chayil as soon as he arrives home. He is then to sit down and learn Torah, avoiding all mundane speech, until he makes Kiddush.
 Admur 271:2; Ketzos Hashulchan 79:2
 So writes Admur ibid; Other Poskim however do not mention that it is a mere Mitzvah Min Hamuvchar and leave room to understand that it is required from the letter of the law. [See Piskeiy Teshuvos 271 footnote 27]
 Admur ibid and 271:16; Michaber 271:1 “When one arrives home he is to eat right away”; Tur 271; M”A 271 “This means to make Kiddush right away”
The reason: As one is to fulfill the Mitzvah of sanctifying Shabbos as soon as possible. [M”B 271:1; Siddur Yaavetz “Zerizin Makdimim Lemitzvos”] Alternatively, it is because Shabbos is similar to the Yovel year, of which the law is that one must say “Mekudash” by its entrance. [See Ramban Shemos 20:8; Rashba 4:295] According to Kabala, the reason is because the Kiddush and meal is the completion of the Tikkun that was performed in the prayer, and hence there should not be an interval between them. [Kaf Hachaim 271:5]
 M”B 271:1
 Chida in Moreh Batzeba 4:146; See Kaf Hachaim 271:5
 Admur 271:16; Pesachim 106:1
 Admur ibid; Taz 271:1; M”A ibid in name of Tikkunei Shabbos that due to Mazal Madim one is to make Kiddush before nighttime; Hagahos Beis Yosef that it is permitted to say Kiddush during daytime; See Ketzos Hashulchan 79 footnote 5 that so is implied also from Bach and M”A
Other opinions: Some Poskim rule one is never to make Kiddush before Tzeis Hakochavim and the Mitzvah to make Kiddush as soon as one arrives home only applies after nightfall. [Elya Raba 271:1; Implication of Bach 270; Shiltei Gibiorim Perek Erev Pesachim, brought in Kaf Hachaim 271:2; Biur Halacha 271:1 “Miyad”]
 Michaber ibid
 The reason: As since one has already accepted Shabbos [through Davening] and added Mechol Al Hakodesh, the entrance of Shabbos has already arrived for him [and it is thus considered that he is making Kiddush on Shabbos itself]. Now, since one is to make Kiddush as close as possible to the entrance of Shabbos, therefore he is to make Kiddush after he leaves Shul as soon as possible, even though it is still day. [ibid]
 Ketzos Hashulchan 79 footnote 5; Biur Halacha 271:1 “Miyad”
 Ketzos Hashulchan 79 footnote 5
 Admur 271:2; M”A 271:1; Rameh Mipuno
 The reason: [Although making Kiddush is a Biblical command and hence should be performed without delay, nevertheless] in such a case one may rely on the fact that he already mentioned Shabbos in its initial entrance during the Shemoneh Esrei of Maariv, and thus already fulfilled his Biblical obligation, as Biblically, one is only required to mention the Shabbos in mere words even without wine, and he has already mentioned it in prayer. [Admur ibid]
 M”B 271:1
 See Poskim brought in Piskeiy Teshuvos 271:3 footnote 31 and other cases of justification in footnote 32
 M”B 271:1
 Piskeiy Teshuvos 271 footnote 36
 Kaf Hachaim 271:2