Why sometimes it takes so long for STOCKHISTORY to pull data?

I just knew STOCKHISTORY a few days ago, then started working on VBA code for stock historical data analysis. I am still testing the code.

I have a list of more than 5000 companies, and I have tested pulling data from Today()-10 to Today(). For the same symbol list and same date parameter. Sometimes it takes no more than 10 minutes (since only 10 calendar days of data), but sometimes it takes ridiculous amount of times (such as right now, Saturday afternoon, I have been waiting for more than 30 minutes, and only about half of symbol list have been pulled into excel). It is still pulling, I have written a separate procedure to calculate the number of symbol data have been pulled, it is making process, but very slowly, sometimes only 2-3 symbols within 5 minutes, sometimes suddenly adding data for around 100 symbols.

Is it because of weekend or nighttime, then it takes longer time to interact with outside data source? I am not sure where data comes from when using function STOCKHISTORY, does Microsoft store the historical data in its own server, or pulling data from third party. Or it is due to Office 365? Office 365 does not "work hard" on weekend? I am not saying that it takes longer on weekends or nighttime, I am just guessing/feeling like that, I have been working with the function for only a few days.

The processing time is significantly different from time to time, I am wondering why. It does show #BUSY!

Thanks.

STOCKHISTORY gets data from a third party company called Refinitiv. I don't know why the performance varies but they probably deal with large amounts of data requests and throttle the output depending on demand. That's just a guess.

Requesting data for 5000 companies is large and probably more than the typical situation they are set up to service from Excel requests. Remember, you are not paying anything additional to get this data.

If you are using this data for stock trading or professional reasons, you probably need to get a paid account with a market information provider.