If possible, give both units a call so they know to expect you, it'll help smooth things out if the second unit has your details already i.e. type, POB, intended route, source, destination could all be provided beforehand. You will probably find the first unit will get similar routing a lot (just a guess but likely) so I'd guess they will be able to accommodate and help make your transition between the zones smooth.
All in all, expect the unexpected, plan for the risk of wasting some time in that leg of your journey. Also remember to enjoy it lol I find RT incredibly rewarding