Materinty allowence

My work has literally just let me know a week before I'm due to go off that I'm not entitled to SMP so now have to apply for materinty allowence.

Anyone had any experiences with this? My partner is self employed (doesn't make anything over the average wage). How long does this process take? I don't think we can afford me being on maternity (not getting paid) while waiting on the MA to get sorted out.