Bike computer startup time seems to vary a LOT between different manufacturers and models. It also changes regularly with firmware updates and ‘optimisations’, sometimes not for the better. In this video I put 16 different cycling GPS computers to the test against the clock to measure their startup time.
NOTE: GPS/satellite lock is a whole other can of worms… One that has a lot more variables. This aside, everyone has to first wait for the initial boot-up sequence before that sync takes place.