What does "lit." mean in boiling point or melting point specification?
Yes, you are correct: “lit.” refers to the literature value.
Usually one would also expect the corresponding reference, but it looks like Merck doesn't attach any to the provided data directly in place.
From The ACS Style Guide, section Reporting Analytical Data [1, p. 274] (emphasis mine):

Melting and Boiling Points
mp 175.5 °C (lit.25 mp 175–176 °C)
mp 225 °C dec
bp 127 °C
Abbreviations: mp, melting point; bp, boiling point; lit., literature value; and dec, decomposition. A full space is used between the number and the unit °C; the
degree symbol is closed up to the C. A superscript number after “lit.” denotes the
number of the reference.

References

The ACS Style Guide: Effective Communication of Scientific Information, 3rd ed.; Coghill, A. M., Garson, L. R., Eds.; American Chemical Society; Oxford University Press: Washington, DC; Oxford; New York, 2006. ISBN 978-0-8412-3999-9. https://doi.org/10.1021/jm068034q