I am not on Lantus so cannot comment, sorry.
Personally, I have missed morning doses before (on a split dose of Levemir 12 hours apart) and only realised after lunchtime... Corrected my BGL with my bolus insulin (Novorapid) until my next basal was due. This does require continuous BGL testing though as to avoid hypos and obviously, hypers.
Good luck and don't worry too much. Keep an eye on your BGL though! I'd suggest readings every one or two hours.
Cheers,
Grant