Where I teach we do not have radar altimeters and all the goodies some other aircraft have. What we teach is to crosscheck the indicated altitude against that published on the approach plate and to start timing the approach. The reasons are as follows:
The height check is to confirm that the correct QNH or QFE is set. It would be a bit eye-watering to attempt to descend to DA with, for example, 1013 set instead 0f 1003.
The approach is timed as a precaution in case the glideslope is lost. The approach can then be continued as a localiser only procedure. On the majority of such approaches which do not have DME the MAP is defined as a time from the OM, hence the timing.
I'm not at all sure about the comment by Square Leg in the previous reply about MDA for a Cat 1 approach. I thought MDA was for a non-precision approach (VOR, NDB). Any full ILS is a precision approach which includes glidepath guidance and therefore is flown down to the Decision Altitude/Height.