New to HMI programming

I've programmed many PLCs, but never an HMI. Now I have a project for a basic text-screen HMI to alter 5 timers on a PLC.

My PLC of choice is Mitsubishi FX, using GX developer. Mitsubishi sell the Beijer terminals over here in the UK for the FX range.

How easy is it to get to grips with an HMI? What do I do? Where do I start?

Pick the Beiger HMI panel that you think best fits your job, then upload a copy of the User Manual for that terminal. Then read the manual from cover to cover at least once, then decide if it works like you thought it would. If so, buy the terminal and the programming software. Then start work.