The MLA follows The Chicago Manual of Style’s rules for hyphening number ranges in modifiers  (“Hyphenation Guide”). When the compound is an adjective, the compound is hyphened, but no hyphen appears between the adjective and the noun it modifies:

five-to-ten-minute intervals

When the compound is a noun, the entire term is hyphened:

nine-to-ten-year-olds

The same principle applies to numerals (5-to-10-minute intervals, 9-to-10-year-olds), but the addition of a symbol, such as a dollar sign, reduces the number of hyphens needed. Just as the dollar symbol transforms a ten-dollar raise into a $10 raise, it transforms a ten-to-fifteen-dollar raise into a $10-$15 raise (“Hyphenation Guide”).

The Chicago Manual and the MLA recommend recasting where hyphenation becomes awkward (“Phrasal Adjectives”). An annual 1%-2% increase gains three hyphens when the time frame is incorporated into the compound, resulting in an awkward “1%-to-2%-a-year increase.” Avoid phrases like “a twenty-five-to-thirty-hour-a-week commitment.” Instead, try “a weekly commitment of twenty-five to thirty hours” or “a commitment of twenty-five to thirty hours a week.”

Read more on hyphens. 

Works Cited

“Hyphenation Guide.” The Chicago Manual of Style, 17th ed., sec. 7.89, U of Chicago P, 2017, www.chicagomanualofstyle.org/book/ed17/part2/
ch07/psec089.html.

“Phrasal Adjectives.” The Chicago Manual of Style, 17th ed., sec. 5.92, U of Chicago P, 2017, https://www.chicagomanualofstyle.org/book/ed17/part2/
ch05/psec092.html.