Have you even discussed this with the colleague who can't make 9am?
Are they aware that you are happy for them to dial in anywhere?
Why cannot they provide you with any eye information in advance?
How do you intend to manage without them if they are on leave, sick, etc.
Are they easily replaced?
Why not speak to them directly and explain, it's a key client meeting that cannot be changed in terms of timing?
Ask for their proposed solutions for their absence? Briefing you or another colleague?
Dialling in slightly later and coming their section later in the call
Dialing into every second call.
If it was monthly and they missed them all, I would understand your concern but is their contribution so fundamentally important every single week, surely not?
Tell them your position and that you are willing to work with them re proposed solutions and see what they suggest? 2 professionals should be able to find some middle ground.