“And when the Sabbath was past.” In this verse, the “Sabbath” is the special Sabbath (Thursday the 15th of Nisan; the first day of the Feast of Unleavened Bread). Thus Mark 16:1 is saying that the special Sabbath was over and the next day, Friday the 16th of Nisan had begun.
When Mark 16:1 says the “Sabbath” was past, it is talking about the first day of the Feast of Unleavened Bread, which was always a special Sabbath, no matter what day of the week it fell on (Leviticus 23:4-7, Numbers 28:16-18). That is why John 19:31 speaks of the first day of Unleavened Bread as a “High Day” or special Sabbath. The Passover Lamb was sacrificed on the 14th of Nisan in the early evening, and that day at sunset the 15th of Nisan started, which was a “special” Sabbath, not the regular weekly Sabbath (we must keep in mind that Jewish days start at sunset).
The women had seen Joseph of Arimathea put Jesus in the tomb without properly preparing his body (Luke 23:55; cp. Matt. 27:60-61; Mark 15:45-47), so now, on Friday the 16th of Nisan, they went to the market and bought and prepared spices. It is important to see the time break between Mark 15:47 when the women watched Joseph of Arimathea, and Mark 16:1, when they went and bought spices. The women had seen that Joseph of Arimathea did not bury Jesus properly, but they did not have time Wednesday night before the start of the special Sabbath that began the Feast of Unleavened Bread to buy the spices because that Sabbath was so close (Luke 23:54). Even if the women had wanted to buy the spices at that time, the stores would have been closed that close to the Sabbath. So the first opportunity they had to buy and prepare the spices was Friday. Nevertheless, they could not take them to the tomb at that time because the tomb was sealed and guarded. The tomb was guarded for three days: Thursday was day one (this was the special Sabbath that started the Feast of Unleavened Bread); Friday was day two, and Saturday, the weekly Sabbath, was day three. That meant the first day the women could expect to get access to the tomb was Sunday, which is when they went to the tomb with the spices (see commentary on Luke 24:1). That the women bought spices on Friday after the special Sabbath on Thursday, explains why Mark 16:1 says the women bought spices after the Sabbath, but Luke 23:56 makes it clear they had them before the Sabbath. They bought them after the special Sabbath on Thursday, but before the weekly Sabbath on Saturday.
The fact that the women needed time to buy and prepare the spices, which they did on Friday, is one of the reasons that there could not have been a Thursday crucifixion. If Jesus was crucified on Thursday then both Friday and Saturday would have been Sabbaths and the women would not have had time to buy and prepare the spices before getting to the tomb early Sunday morning, and furthermore, there would be no way to reconcile the contradiction that they bought spices both before and after the Sabbath. [For more on the women and the two Sabbaths, see commentary on Matthew 12:40].