This interesting study tested afternoon napping effects on BG levels against the same amount of total sleep, but uninterrupted. The outcome: split sleep produces better alertness but worse BG.
This is a technique my 14-year old uses when he can’t get enough sleep
Duke University press release with many details: https://www.duke-nus.edu.sg/news/split-and-continuous-restricted-sleep-schedules-affect-cognition-and-glucose-levels-differently
Link to abstract and full PDF: https://academic.oup.com/sleep/advance-article/doi/10.1093/sleep/zsz037/5316239