Answer: The Gemara (Shabbos 23b) writes that one should not light the Shabbos candles too early or too late. Thus, the Shulchan Aruch (OC 263:4) writes that one shouldn’t light the Shabbos candles before plag hamincha, one and a quarter halachic hours before nacht, as it wouldn’t be apparent that one is lighting them for Shabbos. The Rema adds that if the candles were lit too early, they need to be blown out and relit for Shabbos.
R’ Akiva Eiger (OC 263:4) writes that the Rema only requires relighting the candles if they weren’t lit lekavod Shabbos. While lechatchila one shouldn’t light too early, if one lit early lekavod Shabbos, they have fulfilled their obligation.
The Mishna Berura (263:20; Biur Halacha) argues that R’ Akiva Eiger’s statement applies only to one who lit after plag hamincha. If one lit before plag hamincha, they would need to relight the candles regardless of their intent.R’ Aryeh Zvi Frommer (Eretz Zvi 1:113), however, understands that R’ Akiva Eiger is referring to lighting before plag hamincha lekavod Shabbos. Providing they lit lekavod Shabbos, one wouldn’t need to relight even if they lit before plag hamincha (See Elef Hamagen 610:7).
Similarly, the Aruch Hashulchan (OC 263:19) writes that while it isn’t ideal to light before plag hamincha, if one did so, they wouldn’t need to relight later.
In conclusion, one should not ideally light their Shabbos candles before plag hamincha though if one did so, they wouldn’t need to relight them later.