Tosefet Shabbat – How late may Shabbos be ended?
At the risk of appearing humorous – For instance can one choose to continue Shabbos through yom 2?
Are any halachic difficulties involved in extending Shabbos very long?
According to some sources, one may end shabbos as late as he wants. However technically you will have to end shabbos when you daven maariv, and say Ata Chonantanu. Also it is preferable to eat melava malka before chatzos.
Pri Megadim Eshel Avraham beginning 296, M:B 300-2, see Piskei Teshuvos 293-2 that there are opinions that it can only be for a certain amount of time.