Do I need acclimatisation time before hiking the Inca Trail to Machu Picchu?

Yes, spend at least 2 full days in Cusco (3,400 m) doing easy walking and drinking coca tea before the trek. Most altitude sickness symptoms hit within 12–24 hours and usually settle by day two. The classic 4-day Inca Trail itself tops out at 4,200 m at Dead Woman's Pass.