"Service time" isn't terminology used in CBA 11.19 for the Entry-Level Slide; eligibility for Slide depends solely on the ELC signing age and NHL Games (not) played. Whether the player is in Junior league or not doesn't affect it.
Sign ELC at 18 or 19 (age at Sept 15th that year; 19 y.o. late birthday guys are an exception and not eligible), you will slide the first season under that ELC unless you play 10+ games in NHL. Sign ELC at 18 and Slide your first season, you're eligible for another Slide if you still won't play 10+ games in NHL. Playing in AHL doesn't burn any young player's ELC.
Europe guys are just as eligible for Entry-Level Slide as anyone, but the European-drafted guys have their own quirk from the NHL/IIHF transfer agreement, by which guys under 20 if they are under a contract to an IIHF-associated league and if they don't make it to the NHL roster and would be sent down to AHL, the European team has the first dips to demand the young player being sent back to service his contract there. Quite often the Euro teams seem to sign promising youngsters at 17 for multi-year contracts to get their hand on the sweet transfer agreement moolah in the likely case he gets drafted and signed.
Case in point: Kuokkanen slided his first in 2017-18. Having signed at 19, he's not eligible for another slide. As we remember Sebastian Aho's dad threatened that a year in AHL wasn't an option and that they would call him back to Kärpät. But they didn't in the end.
Janne Kuokkanen - CapFriendly - NHL Salary Caps
Case 2: Gauthier and Entry-lever Slide re CHL -> AHL:
He slided 2016-17 playing in CHL and slided again 2017-18 playing in AHL. BUT, despite this the AHL year nevertheless counts as a professional season for the Expansion Draft purposes due to the underager CHL/AHL transfer rules.
Julien Gauthier - CapFriendly - NHL Salary Caps
Case 3: Necas. Signed at 18, slided 2017-18 playing in Europe, is still eligible for another slide.
Martin Necas - CapFriendly - NHL Salary Caps