If you have a 24 hour clock then seeing 08:00 with or without a colon certainly means AM since anything below 12 is AM, it's not the colon that really reflects or affects that just the number which is rather easy to tell with or without a colon.I work in the medical sector and have never seen a colon. I guess because it's military time and that's not exactly the same as 24h time. It looks wrong to me. I work night shift sometimes and if I wake up and my phone says 8:00 I sometimes question if it's 8am or 8pm. If it says 0800 I know it's 8am vs 2000. In the AM times the colon throws me off.
That said, that's basically one of the differences between military time and regular 24 hour time (which is what the iPhone and most devices typically support).