No, you cannot decline the Total Power observations to reduce the total time required for the proposal.
The OT automatically computes whether or not 7-m Array and Total Power (TP) observations are necessary based on the 'Largest Angular Structure in source' (LAS) entry in the Control & Performance editor. If the requested LAS is larger than that achievable by the ACA 7-m array alone, Total Power (TP) observations will be added if possible i.e. for spectral line observations in Bands 1, 3-8; for continuum and higher-frequency observations the TP array is not currently offered. Users may not reject the scheduling of TP observations because they have access to single dish data from other telescopes. The rationale behind this is that the ALMA archive should provide the best and most complete dataset possible to future archival researchers, including TP data when needed.