Advil Liqui-Gels is a brand of ibuprofen, a nonsteroidal anti-inflammatory drug (NSAID) used to relieve pain and reduce fever. According to the sources provided, the onset of action of Advil Liqui-Gels varies from person to person and depends on several factors.

GoodRx reports that ibuprofen generally takes about 30 minutes to start working and reaches its peak effect after 1-2 hours. However, the duration of the effect varies from 4 to 6 hours depending on the dose and the individual's metabolism.

Drug Patent Watch states that the absorption of ibuprofen is rapid and complete, with peak plasma concentrations reached within 1-2 hours after oral administration.

A study published in the journal Clinical Pharmacokinetics [3] found that the onset of action of ibuprofen was faster when taken in a liquid form than in a tablet form. The study also showed that the maximum concentration of ibuprofen in the blood was higher when taken in a liquid form.

In summary, Advil Liqui-Gels work quickly due to the rapid and complete absorption of ibuprofen in the liquid form. However, the onset of action and duration of effect may vary depending on the individual's metabolism and the dose taken.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/ADVIL
[2] https://www.goodrx.com/ibuprofen/how-long-does-ibuprofen-take-to-work
[3] https://pubmed.ncbi.nlm.nih.gov/27806251/